The brain is able to let us see objects at a generally constant color eventhough the objects may be viewed at a variety of light conditions. For instance a vegetable like a cucumber on a sunny day allows us to know that its color is green. If the day were to be cloudy, since there is not as much light intensity we should 'see' a different color for the cucumber but we still 'think' it is green. Maybe this kind of constancy was for simplicity so that we would not become so confused with the endless variety of colors that can be portrayed with different light intensities. Maybe the identification of limited number of colors is a form of adaptation which has evolved through time.

The three major pigments in the cone cells of the retina allow us to categorize the colors of objects. But what is the significant purpose of color? Color does not seem to be such an essential factor for survival. Those who are color blind seem to function well in everyday life. Just seeing black and white does not affect the clarity of the objects I have personally seen.

Since there exists numerous wavelengths for the color spectrum, different organisms have access to different colors. What we see as a cucumber may look as a different color to certain organisms. Certain insects for example see different wavelengths of color around flowers in which we humans are unable to detect with our own eyes. Maybe we do not need to see such explicit colors in order for us to survive. The three pigments which interact to show us the colors we 'see' may be the the only colors we need to function in this world. It is also said that individuals may have different opinions about a certain color. Through my experience I have had instances where another person and I disagreed on what the color was for an object. Are there individual differences for seeing color?

Yes, there are indeed (for a variety of reasons) likely to be individual differences in characterizing the color of something. For all the reasons you give (and more), what "color" corresponds to is a pattern of activity in your brain, and the same input may cause different patterns in other peoples' brains (or even in yours, at different times; at night, for example, photons of a particular wavelength don't create a sense of color). The purpose of color? Presumably it helps us survive, as you say, but that doesn't take one very far. All organisms that currently exist have internal organizations that help them survive and, as you point, out these involve a variety of different "color senses", so it certainly isn't true that there is any "best" one. Clearly, though, color sense helps us to discriminate things we couldn't otherwise discriminate (red lights and green lights, for example). And, in this sense, people with color blindness have a "deficit". Correspondingly, all of us would in fact see "less clearly" if we worked only in light intensity (black and white) without being able to discriminate wavelengths. PG