i've often thought about this one myself! i think it's a really interesting concept?! Perception of color See also: Grue (color) The question hinges on whether color is a product of the mind or an inherent property of objects. While most philosophers will agree that color assignment corresponds to light frequency, it is not at all clear whether the particular psychological phenomena of color are imposed on these visual signals by the mind, or whether such qualia are somehow naturally associated with their noumena. Another way to look at this question is to assume two people ("Fred" and "George" for the sake of convenience) see colors differently. That is, when Fred sees the sky, his mind interprets this light signal as blue. He calls the sky, "blue." However, when George sees the sky, his mind assigns green to that light frequency. If Fred were able to step into George's mind, he would be amazed that George saw green skies. However, George has learned to associate the word, "blue" with what his mind sees as green, and so he calls the sky, "blue," because for him the color green has the name, "blue." The question is whether blue must be blue for all people, or whether the perception of that particular color is assigned by the mind.