In the eye of the beholder: Is color classification consistent among human observers?

Colorful displays have evolved in multiple plant and animal species as signals to mutualists, antagonists, competitors, mates, and other potential receivers. Studies of color have long relied on subjective classifications of color by human observers. However, humans have a limited ability to perceive color compared to other animals, and human biological, cultural, and environmental variables can influence color perception. Here, we test the consistency of human color classification using fruit color as a model system. We used reflectance data of 67 tropical fruits and surveyed 786 participants to assess the degree to which (a) participants of different cultural and linguistic backgrounds agree on color classification of fruits; and (b) human classification to a discrete set of commonly used colors (e.g., red, blue, green) corresponds to natural clusters based on light reflectance measures processed through visual systems of other animals. We find that individual humans tend to agree on the colors they attribute to fruits across language groups. However, these colors do not correspond to clearly discernible clusters in di- or tetrachromatic visual systems. These results indicate that subjective color categorizations tend to be consistent among observers and can be used for large synthetic studies, but also that they do not fully reflect natural categories that are relevant to animal observers.