Orthogonal Relations and Color Constancy in Dichromatic Colorblindness

This paper employs uniform color space to analyze relations in dichromacy (protanopia, deuteranopia, tritanopia). Fifty percent or less of dichromats represent the classical reduction form of trichromacy, where one of three cones is inoperative but normal trichromatic color mixture such as complementary colors (pairs that mix white) are accepted by the dichromat, whose data can thus be plotted to CIE chromaticity spaces. The remaining dichromats comprise many and varied more-complex gene arrays from mutations, recombinations, etc. Though perhaps a minority, the three reductionist types provide a simple standard, in genotype and phenotype, to which the more complex remainder may be compared. Here, previously published data on dichromacy are plotted and analyzed in CIELUV uniform color space to find spatial relations in terms of color appearance space (e.g., hue angle). Traditional residual (seen) hues for protanopia and deuteranopia (both red–green colorblindness) are yellow and blue, but analysis indicates the protanopic residual hues are more greenish yellow and reddish blue than in tradition. Results for three illuminants (D65, D50, B) imply four principles in the spatial structure of dichromacy: (1) complementarity of confusion hue pairs and of residual hue pairs; (2) orthogonality of confusion locus and residual hues locus at their intersection with the white point, in each dichromatic type; (3) orthogonality of protanopic and tritanopic confusion loci; and (4) inverse relations between protanopic and tritanopic systems generally, such that one''s confusion hues are the other''s residual hues. Two of the three dichromatic systems do not represent components of normal trichromatic vision as sometimes thought but are quite different. Wavelength shifts between illuminants demonstrate chromatic adaptation correlates exactly with that in trichromatic vision. In theory these results clarify relations in and between types of dichromacy. They also apply in Munsell and CIELAB color spaces but inexactly to the degree they employ inexact complementarity.     

Comparative use of color vision for frugivory by sympatric species of platyrrhines

Ateles spp. and Alouatta spp. are often sympatric, and although they are mainly frugivorous and folivorous, respectively, they consume some of the same fruit species. However, they differ in terms of color vision, which is thought to be important for fruit detection. Alouatta spp. have routine trichromatic color vision, while Ateles spp. presents the classic polymorphism of platyrrhines: heterozygous females have trichromatic color vision, and males and homozygous females have dichromatic vision. Given these perceptual differences, one might expect Alouatta spp. to consume more reddish fruits than Ateles spp., since trichromats have an advantage for detecting fruits of that hue. Furthermore, since Ateles spp. have up to six different color vision phenotypes, as do most other platyrrhines, they might be expected to include fruits with a wider variety of hues in their diet than Alouatta spp. To test these hypotheses we studied the fruit foraging behavior of sympatric Alouatta palliata and Ateles geoffroyi in Costa Rica, and modeled the detectability of fruit via the various color vision phenotypes in these primates. We found little similarity in fruit diet between these two species (Morisita = 0.086). Furthermore, despite its polymorphism, A. geoffroyi consumed more reddish fruits than A. palliata, which consumed more greenish fruits. Our modeling results suggest that most fruit species included in the diet of A. geoffroyi can be discriminated by most color vision phenotypes present in the population. These findings show that the effect of polymorphism in platyrrhines on fruit detection may not be a disadvantage for frugivory. We suggest that routine trichromacy may be advantageous for other foraging tasks, such as feeding on young leaves.     

Cone Photoreceptor Sensitivities and Unique Hue Chromatic Responses: Correlation and Causation Imply the Physiological Basis of Unique Hues

This paper relates major functions at the start and end of the color vision process. The process starts with three cone photoreceptors transducing light into electrical responses. Cone sensitivities were once expected to be Red Green Blue color matching functions (to mix colors) but microspectrometry proved otherwise: they instead peak in yellowish, greenish, and blueish hues. These physiological functions are an enigma, unmatched with any set of psychophysical (behavioral) functions. The end-result of the visual process is color sensation, whose essential percepts are unique (or pure) hues red, yellow, green, blue. Unique hues cannot be described by other hues, but can describe all other hues, e.g., that hue is reddish-blue. They are carried by four opponent chromatic response curves but the literature does not specify whether each curve represents a range of hues or only one hue (a unique) over its wavelength range. Here the latter is demonstrated, confirming that opponent chromatic responses define, and may be termed, unique hue chromatic responses. These psychophysical functions also are an enigma, unmatched with any physiological functions or basis. Here both enigmas are solved by demonstrating the three cone sensitivity curves and the three spectral chromatic response curves are almost identical sets (Pearson correlation coefficients r from 0.95–1.0) in peak wavelengths, curve shapes, math functions, and curve crossover wavelengths, though previously unrecognized due to presentation of curves in different formats, e.g., log, linear. (Red chromatic response curve is largely nonspectral and thus derives from two cones.) Close correlation combined with deterministic causation implies cones are the physiological basis of unique hues. This match of three physiological and three psychophysical functions is unique in color vision.     

Visual detection and fruit selection by the mantled howler monkey (Alouatta palliata)

Howler monkeys (platyrrhini) have evolved routine trichromatic color vision independently from catarrhines, which presents an opportunity to test hypotheses concerning the adaptive value of distinguishing reddish from greenish hues. A longstanding hypothesis posits that trichromacy aids in the efficient detection of reddish-ripe fruits, which could be an advantage for the detection of the nutritional content of the fruit, such as sugars. In the present study, we assessed fruit visual conspicuity and selection based on color and sucrose content by wild mantled howler monkeys (Alouatta palliata) on Agaltepec Island, Mexico. We used colorimetry to classify dietary fruits as cryptic (greenish) or conspicuous (reddish) against their background leaves. Species-specific color models indicate that trichromatic howler monkeys should be more efficient in discriminating the conspicuous ripe fruits from leaves compared to detecting cryptic ripe fruits from leaves. We found howler monkeys consume more cryptic fruits compared to conspicuous fruits, and that they consume more unripe fruits than ripe fruits. The consumption (acceptance) of fruit was independent of sucrose content, and thus this disaccharide may not play an essential role in mantled howler food selection. Our findings suggest that routine trichromatic color vision may aid in the detection and discrimination of conspicuously colored fruits, but that the final decision whether to accept or reject a fruit probably involves the use of other senses in addition to vision.     

Fig Foraging by Dichromatic and Trichromatic <Emphasis Type="Italic">Cebus capucinus</Emphasis> in a Tropical Dry Forest

Figs are important resources for frugivores, and Ficus is an ideal taxon for evaluating patterns of primate foraging related to food color. Ficus spp. can be classified as conspicuous (color change from greenish to reddish during ripening) or cryptic (green throughout ripening). To investigate the effect on foraging of color vision phenotype variation for these 2 types of figs, we conducted a 20-mo study on 4 groups of white-faced capuchins (Cebus capucinus) in the Santa Rosa Sector of the ACG, Costa Rica between May 2004 and September 2008. We genotyped all individuals and collected behavioral data on feeding rates, acceptance indices, and foraging sequences. We found a significant effect of fig type; feeding rates and acceptance indices were higher for conspicuous figs than for cryptic figs, and subjects sniffed cryptic figs more often than conspicuous figs. We also found that dichromats sniffed more figs and had longer foraging sequences than trichromats, especially for cryptic figs. Among 6 subtypes of dichromats and trichromats, monkeys possessing the trichromat phenotype with the most spectrally separated L-M opsin alleles showed the highest acceptance index for conspicuous figs, though there were no differences in feeding rates among phenotypes. We conclude: 1) conspicuous figs are visually salient not only for trichromats but also for dichromats, 2) olfaction is important for evaluating edibility of cryptic figs, and 3) the reliance on olfaction for selecting fruit is greater in dichromats. These results indicate divergent foraging strategies among color vision phenotypes for assessing food items.     

Color discrimination by the cotton-top tamarin (Saguinus oedipus oedipus) and its relation to fruit coloration

Old World monkeys and apes have been reported to differ from New World monkeys in their abilities to discriminate colors across the visible spectrum. Old World monkeys and apes (Macaca, Pan, Pongo) discriminate colors quite accurately, while some New World monkeys studied (Saimiri, Cebus) have shown lower sensitivity to and poorer discrimination of long wavelength light. This study examined the color discrimination ability of another New World primate, the cotton-top tamarin, Saguinus oedipus oedipus (family Callitrichidae). The tamarins were trained to discriminate a set of Munsell color chips, both within the same hue category and from the 2 hue categories on either side of the training hue. Results indicated that the cotton-top tamarin can make accurate discriminations across the visible spectrum. Human subjects were tested under similar conditions in order to compare their color discrimination abilities to those of the tamarins. The tamarins and human subjects had the most difficulty discriminating the same hues. The discrimination abilities of the monkeys were assessed in relation to the coloration of fruits eaten in a natural environment. A list of the species of fruits commonly eaten by various species of New World monkeys was compiled and the coloration of fruits at maturity was noted. It was found that most New World primate species eat fruits whose mature coloration ranges across most of the spectrum.     

Reaction times identify a Pavlovian component in a two-choice discrimination

Six pigeons discriminated on discrete trials between two colors. In Experiment 1, two luminous spots were both either blue or green and the reinforced responses were “peck left” for blue and “peck right” for green. In Experiment 2, the hue of a center spot controlled subsequent choice pecks to left or right. In both experiments response bias was manipulated in two ways. During stimulus frequency (“SF”) sessions correct responses brought food on 40% of trials; in “imbalanced” blocks of sessions one hue appeared on 80% of trials and the other on 20%. During reinforcement probability (“RNF”) sessions the hues appeared equally often, but in imbalanced blocks the hues signaled different reinforcement probabilities, either 64% or 16%. In “balanced” control blocks the hues appeared equally often and were both reinforced at 40%. The experiments gave similar results. When bias was computed from choice percentages the imbalanced conditions yielded substantial response bias, and the amount of bias was about the same under RNF and SF treatments. However, reaction times (RTs) gave a different outcome. RNF imbalance slowed responses directed at the less reinforced stimulus, but SF imbalance had little RT effect (Experiment 1) or no effect (Experiment 2). These results suggest that choice was controlled by an instrumental stimulus-response-reinforcement association, whereas RTs were controlled by a Pavlovian stimulus-reinforcement association.     

Simulation of water colors in a shallow acidified lake, Lake Onneto, Japan, using colorimetric analysis and bio-optical modeling

Lake Onneto has unusually brilliant water colors, such as blue-green, green, and greenish yellow. We investigated the coloration mechanism in this lake by measuring the radiometric water color and inherent optical properties (IOPs), such as attenuation, absorption, and scattering coefficients of color-producing agents (CPAs) in the lake. The hue of the water body was determined using colorimetric analysis. In addition, the radiometric water color of the lake was simulated using bio-optical modeling. Results showed that the hues of the water body were different between two sampling stations (blue-green and green at 3.1 and 5.5 m of bottom depth, respectively). However, the total suspended solids (TSS) concentrations were almost identical between the two stations (0.47 and 0.42 mg l⁻¹, respectively). In addition, the attenuation and absorption coefficients showed that the CPAs in the water body were only inorganic suspended solids (ISS) more than 0.7 μm in diameter, and specific CPAs, such as dissolved mineral ions and aqueous colloids, were not observed in the lake. Simulation of the radiometric water color showed that the radiation around 600 nm of wavelength (yellow region) steeply increased with decreasing bottom depth, indicating that the water colors of Lake Onneto are strongly governed by the light reflection from yellowish bottom sediments.     

Exceptional three-dimensional preservation and coloration of an originally iridescent fossil feather from the Middle Eocene Messel Oil Shale

A feather from the Eocene Messel Formation, Germany, has been demonstrated to have been originally structurally colored by densely packed sheets of melanosomes similar to modern iridescent feathers exhibiting thin-film diffraction. The fossil itself currently exhibits a silvery sheen, but the mechanism for generating this optical effect was not fully understood. Here we use scanning electron microscopy, electron probe microanalysis, and dual-beam focused ion beam scanning electron microscopy to investigate the source of the silvery sheen that occurs in the apical feather barbules. Focused ion beam scanning electron microscopy provides a powerful tool for studying three-dimensionality of nanostructures in fossils. Use of the method reveals that the flattened apical barbules are preserved almost perfectly, including smooth structural melanosome sheets on the obverse surface of the fossil feather that are identical to those that cause iridescence in modern bird feathers. Most of each apical barbule is preserved beneath a thin layer of sediment. The silvery sheen is generated by incoherent light diffraction between this sediment layer and melanosomes and, although related to the original iridescence of the feather, is not a feature of the feather itself. The reddish and greenish hues frequently exhibited by fossil feathers from the Messel Formation appear to be due to precipitates on the surface of individual melanosomes.     

Texture segregation in chromatic element-arrangement patterns.

An element-arrangement pattern is composed of two types of elements arranged differently in different regions of a pattern. Rapid texture segregation depends on spontaneously discriminating the difference in the arrangement of the elements. Five experiments investigated the perceived segregation of patterns composed of two types of squares arranged in vertical stripes in the top and bottom regions and in a checkerboard arrangement in the middle region. The squares were either equal in luminance and different in hue or equal in hue and different in luminance. The rated similarities of the two hues in a pattern failed to predict perceived segregation. For a given background luminance, the perceived segregation was predicted by the square-root of the sum of the squares of the differences in the outputs of the L - M + S and L + M - S opponent channels, where L, M, and S were the cone contrasts of the long-, medium-, and short-wavelength receptors. The perceived similarity of the two hues in a pattern was not affected by the background luminance but was a function of cone excitations instead. For patterns differing in hue and equal in luminance, perceived segregation was an inverse function of the background luminance. A white background decreased the perceived segregation, but a black background did not. The effect of background luminance was not on the discrimination of the individual hues. The two hues making up a texture pattern were clearly distinguishable on a white background. A white background interfered with the discrimination of the vertical and diagonal columns of squares that distinguished the texture regions. For patterns differing in luminance and equal in hue, black and white backgrounds decreased the perceived segregation. The results indicate that adapting to an achromatic luminance distant from the luminance of the squares increased the Weber threshold for discriminating luminance differences, but did not increase the Weber threshold for discriminating hue differences. The experiments also revealed that luminance was the primary factor affecting perceived segregation and that perceived brightness is secondary. The results are consistent with the hypothesis that perceived segregation in element-arrangement patterns is primarily a function of the differences in the outputs of relatively early filtering mechanisms that encode pattern differences prior to the specification of the element shapes and their properties.     

Trying to See Red Through Stickleback Photoreceptors: Functional Substitution of Receptor Sensitivities

A key to understanding animal behavior is knowledge of the sensory information animals extract from their environment. For visually motivated tasks, the information animals obtain through their eyes is often assumed to be essentially the same as that perceived by humans. However, known differences in structure and processing among the visual systems of different animals clearly indicate that the world seen by each is different. A well‐characterized difference between human and other animal visual systems is the number of types and spectral sensitivities of their photoreceptors. We are developing a technique, functional substitution, that exploits knowledge of these differences to portray for human subjects, colors as they would appear through the photoreceptors of another animal. In a specific application, we ask human subjects to rank hues of male threespine stickleback (Gasterosteus aculeatus) throats viewed through stickleback photopigments. We compare these ranks to ranks of the same throat hues viewed through normal human photoreceptors. We find essentially no difference between the two sets of rankings. This suggests that any differences in human and stickleback rankings of such hues would result from differences in post‐receptoral neural processing. Using a previously developed model of stickleback neural processing, we established another ranking of the hues which was again essentially the same as the rankings produced by the human subjects. A growing literature indicates that stickleback do rank such hues in the evaluation of males as potential mates or threats. Although our results do not demonstrate that humans and stickleback use the same mechanisms to assess color, our experiments significantly failed to show that stickleback and human rankings of throat hues should be different. Nevertheless, a comparison of all these rankings to ranks derived from subjective color scoring by human observers suggests that color scoring may utilize other cues and should thus be used cautiously.     

Dichromats detect colour-camouflaged objects that are not detected by trichromats.

To explain the surprisingly high frequency of congenital red-green colour blindness, the suggestion has been made that dichromats might be at an advantage in breaking certain kinds of colour camouflage. We have compared the performance of dichromats and normal observers in a task in which texture is camouflaged by colour. The texture elements in a target area differed in either orientation or size from the background elements. In one condition, the texture elements were all of the same colour; in the camouflage condition they were randomly coloured red or green. For trichromats, it proved to be more difficult to detect the target region in the camouflage condition, even though colour was completely irrelevant to the task. Dichromats (n = 7) did not show this effect, and indeed performed better than trichromats in the camouflage condition. We conclude that colour can interfere with segregation based upon texture, and that dichromats are less susceptible to such interference.     

Form perception and visual acuity in a chimpanzee

A 6.5-year-old female chimpanzee learned to distinguish perfectly every letter of the alphabet in a matching-to-sample task with 26 letters as choice alternatives. Confusion of letters during the initial training was used to scale them in a multidimensional similarity space and to associate them in hierarchical clusters. The results resembled those obtained from similarity judgements by humans. Using letters of various sizes, a visual acuity test revealed that the chimpanzee's acuity was about 1.5, comparable to that in normal humans. The chimpanzee also readily learned to use letters as names of individual humans and chimpanzees. A species-typical feature was identified in the perceptual processes associated with complex forms, such as those involved in individual recognition.     

Unconscious letter discrimination is enhanced by association with conscious color perception in visual form agnosia

Adaptive behavior guided by unconscious visual cues occurs in patients with various kinds of brain damage as well as in normal observers, all of whom can process visual information of which they are fully unaware [1] [2] [3] [4] [5] [6] [7] [8]. Little is known on the possibility that unconscious vision is influenced by visual cues that have access to consciousness [9]. Here we report a 'blind' letter discrimination induced through a semantic interaction with conscious color processing in a patient who is agnosic for visual shapes, but has normal color vision and visual imagery. In seeing the initial letters of color names printed in different colors, it is normally easier to name the print color when it is congruent with the initial letter of the color name than when it is not [10]. The patient could discriminate the initial letters of the words 'red' and 'green' printed in the corresponding colors significantly above chance but without any conscious accompaniment, whereas he performed at chance with the reverse color-letter mapping as well as in standard tests of letter reading. We suggest that the consciously perceived colors activated a representation of the corresponding word names and their component letters, which in turn brought out a partially successful, unconscious processing of visual inputs corresponding to the activated letter representations.     

Contributions of pterin and carotenoid pigments to dewlap coloration in two anole species

Animals can acquire bright coloration using a variety of pigmentary and microstructural mechanisms. Reptiles and amphibians are known to use two types of pigments - pterins and carotenoids - to generate their spectrum of colorful red, orange, and yellow hues. Because both pigment classes can confer all of these hues, the relative importance of pterins versus carotenoids in creating these different colors is not always apparent. We studied the carotenoid and pterin content of red and yellow dewlap regions in two neotropical anole species - the brown anole (Norops sagrei) and the ground anole (N. humilis). Pterins (likely drosopterins) and carotenoids (likely xanthophylls) were present in all tissues from all individuals. Pterins were more enriched in the lateral (red) region, and carotenoids more enriched in the midline (yellow) region in N. humilis, but pterins and carotenoids were found in similar concentrations among lateral and midline regions in N. sagrei. These patterns indicate that both carotenoid and pterin pigments are responsible for producing color in the dichromatic dewlaps of these two species, and that in these two species the two pigments interact differently to produce the observed colors.     

Observations on the colours of lumpsuckers, Cyclopterus lumpus L.

Ripe unfertilized eggs derived from fish landed at two Icelandic ports were predominantly red and yellow-red, but a small proportion were red-purple. There was a significant difference between the frequencies of hues of eggs from the two landing places. During the phase of blastula formation, fertilized red-purple eggs showed no discernible change in either hue or chroma. However, as the gastrula formed and covered the yolk, the chroma declined dramatically, although the hue remained unaltered. When the embryo formed, the chroma continued to decrease and the hue also began to change as the red-purple pigment disappeared from the yolk and the orange-yellow oil of the yolk became more visible.
The most common plasma colouration in male fish collected at Hafnarfjordur and Husavik was red, but the observed hues covered 60% of the visible spectrum, ranging from green to purple. No significant differences between Hafnarfjordur and Husavik males in terms of hue or value were discerned, but there was a significant difference in chroma score. Female plasma hues were almost as variable as the males (spanning 45% of the visible spectrum) but centred in the green-yellow zone. Plasma, subcutaneous jelly and skin colours were closely linked.
Fish from the oceanic feeding grounds were all green in skin colour, whatever their age or sex; it is suggested that this colouration has a cryptic function in the near surface waters inhabited by lumpsuckers.     

Effect of color hue and brightness of artificial oviposition substrates on the selection of oviposition site by Dacus oleae

In laboratory experiments of the choice type, olive fruit flies, Dacus oleae (Gmelin), wild and/or olivereared for a few generations, showed strong preference for oviposition in yellow and orange colored ceresin wax domes 18 mm in diameter. Green colored domes of two different hues were less preferred, while red, blue, black and white domes received a limited number of eggs when a preferred color was present. The females more frequently visited the domes of the preferred colors, which indicates that they selected them before arrival. The observed preference for certain colors like yellow and orange depended primarily on the color hue and not on the intensity of the total reflected light or on the degree to which the colored domes contrasted with the background. The females responded positively to hues reflecting maximally between 560 and 610 nm, optinum at ca. 580 nm. Hues reflecting maximally between 520 and 550 nm or above 610 nm were not very attractive while hues reflecting below 520 nm and especially between 400 and 480 nm appeared to be rather unattractive. There were indications that not only the spectral purity of a hue but also the quantity of the energy reflected within the narrow spectral region which corresponds to that hue are important for the selection of the oviposition site by this fly.

---

Der einfluss von farbtönen und farbintensität künstlicher eiablagesubstrate auf ihre auswahl für die eiablage bei Dacus oleae

Zusammenfassung In Auswahlversuchen im Labor bevorzugten wilde und für einige Generationen im Labor auf Oliven gezüchtete Olivenfliegenweibchen zur Eiablage gelb und orange gefärbte Ceresinwachsdome von 18 mm Durchmesser. Grüngefärbte Dome von zwei verschiedenen Farbtönen waren weniger bevorzugt. Rote, blaue, schwarze und weisse Dome wurden mit einer begrenzten Anzahl Eiern belegt, wenn eine der bevorzugten Farben dabei war. Die Weibchen besuchten öfter die Dome mit den bevorzugten Farben, was darauf hindeutet, dass sie diese vor der Ankunft auswählten.Die beobachtete Bevorzugung für gewisse Farben wie gelb und orange hing hauptsächlich von den Farbtönen ab und nicht von der Intensität des total reflektierten Lichtes oder der Stärke des Kontrastes der farbigen Dome vom Hintergrund. Die Weibchen reagierten positiv auf Farbtöne mit einer maximalen Reflektion zwischen 560 und 610 nm mit einem Optimum bei ca. 580 nm. Farbtöne, die maximal zwischen 520 und 550 nm oder bei mehr als 610 nm reflektierten, waren nicht sehr attraktiv und Farbtöne mit einer Reflektion bei weniger als 520 nm, speziell zwischen 400 und 480 nm, scheinen nicht attraktiv zu sein. Es bestehen Hinweise dafür, dass nicht nur die Farbreinheit sondern auch die Menge der reflektierten Energie des entsprechenden Spektralabschnittes wichtig für die Auswahl der Eiablagesubstrate ist.

     

Perception Of Color As A Function Of The Combined Effect Of The Surroundings And A Test Field

The wide variety of shades of color that a human being is capable of perceiving consists of pigment colors, a considerable number of which are colors with gray and black hues. Only some of this wide variety of colors may be reproduced by the use of isolated autoluminescent sources of radiation: colors with dark shades cannot be produced. Under what possible conditions, we may ask, can the entire range of pigment colors be reproduced by luminescent sources of radiation?     

A behavioral odor similarity "space" in larval Drosophila

To provide a behavior-based estimate of odor similarity in larval Drosophila, we use 4 recognition-type experiments: 1) We train larvae to associate an odor with food and then test whether they would regard another odor as the same as the trained one. 2) We train larvae to associate an odor with food and test whether they prefer the trained odor against a novel nontrained one. 3) We train larvae differentially to associate one odor with food, but not the other one, and test whether they prefer the rewarded against the nonrewarded odor. 4) In an experiment like (3), we test the larvae after a 30-min break. This yields a combined task-independent estimate of perceived difference between odor pairs. Comparing these perceived differences to published measures of physicochemical difference reveals a weak correlation. A notable exception are 3-octanol and benzaldehyde, which are distinct in published accounts of chemical similarity and in terms of their published sensory representation but nevertheless are consistently regarded as the most similar of the 10 odor pairs employed. It thus appears as if at least some aspects of olfactory perception are "computed" in postreceptor circuits on the basis of sensory signals rather than being immediately given by them.     

Dichromatic and Trichromatic Callithrix geoffroyi Differ in Relative Foraging Ability for Red-Green Color-Camouflaged and Non-camouflaged food

An advantage for trichromatic color vision in primates is shown by its presence in many lineages, but little attention has been paid to the potential disadvantages of trichromacy. Most New World monkey species are polymorphic for color vision, with both dichromats and trichromats present within a single population. We tested the foraging ability of trichromatic and dichromatic Geoffroy's marmosets (Callithrix geoffroyi) for colored cereal balls (Kix®) under conditions of red-green color camouflage (orange/green Kix® against an orange/green background) or lack of camouflage (Kix® same color as background) in a naturalized captive setting. In separate experiments designed to test foraging ability at long distances (<6 m) and short distances (<0.5 m), trichromats found significantly fewer Kix® under the camouflage condition than in the non-camouflage condition. In contrast, there is no difference in the ability of dichromats to detect color-camouflaged versus non-camouflaged Kix®. There is no significant difference between dichromats and trichromats for either camouflaged or non-camouflaged Kix®, though the power in the tests is low because of high individual variation. The results have clear implications for the foraging strategies of trichromatic marmosets. Differences in intensity of competition between trichromats and dichromats for items of food of different colors in relation to background may also have consequences for the foraging behavior of dichromats.