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I asked this question in the last class but I don't think it was ever really answered. When we discussed color, the general belief came to be that there is only color if someone has the appropriate photoreceptors that can be appropriately stimulated. If the tree falls and no one is around to hear it, there is no sound- then if no one sees a color, there is no color. (?) If this is so, then why are colors so important- particularly as warning signs? In nature animals and plants that have a red or yellow/orange pigment, like frogs, butterflies or certain plants, are generally considered or perceived to be poisonous not only by humans but by other animals. If colors are only a creation of photoreceptors and our brain, then why are they used to signal harmful toxins and protect certain animals throughout nature- not just to humans?