I am having trouble with secondary qualities, which are manufactured in the brain after receipt of digital signals from the sense organs. For example, if I see a green leaf, I know that chlorphyll molecules in the leaf transmit electromagnetic radiation of a frequency such as to produce a sensation of green in my brain. The problem is that all the empirical objects that I perceive are structures of secondary qualities, and these are all outside my head. So where are secondary qualities, inside my head, or outside?

I don't know how much this will help, but there seem to be three things associated with the color green: the experience of green inside your head; the disposition of certain surfaces to produce that experience, something which is not inside your head though it is defined in terms of something inside your head; and the molecular structure of certain surfaces out there that help to cause experiences of green. Most philosophers agree that all three of these things exist, but they disagree about which of them should be identified with 'the color green'.

The color of something is the color of the spectrum that isn't taken in by an object. However when I look at the color "green", do I see the same tint someone sees when they see "blue"? The identification of a color is what we've been told, and we've essentially been told what colors don't go good together. So how do we know that all of our eyes see the same thing? -Samantha B.

This is a classic pr0blem in philosophy, the problem of 'spectrum inversion'. Even if you see blue like I see red, and vice versa, it is very difficult to see how we could ever tell. I cannot see your experiences, and you would use the words 'blue' and 'red' the same way I do, since you were taught to say 'blue' when you saw blue objects and 'red' when you saw red objects, even if your experiences were different. It's interested that spectrum inversion is different from color-blindness. There we can tell, because color blind people can make fewer discriminations.

How can we be sure that we perceive color the same way? In other words, how do I know that the red I see looks the same as the red that you see? We are taught from birth to identify red objects as red, but what if what someone calls red really looks green for example, yet they only call it red because that is what has been taught?

This is the classic skeptical worry about 'spectrum inversion'. Not allphilosophers would agree (surprise, surprise), but I am inclined to saythat you can't know for sure. And I agree with you that the fact thatwe agree about the name of the color doesn't help much. At the sametime, I think we may have good reason to believe that similar coloursare experienced similarly by different people, insofar as we have goodreason to believe that they go through similar neurophysiologicalprocesses when they are exposed to light of the same frequency.

How would you explain the color green to a blind child?

It might also be useful to distinguish the color green from the experience of that colour. Some philosophers (and scientistists, e.g. Galileo) have held that the color just is the experience, but it is m0re common and more plausible to distinguish them. Some would identify the colour with a disposition to produce the experience (which is distinct from experience itself, since it may be present in the dark), some would identify the colour with physical properties of the surfaces of objects, and there are other views as well. Anyway, if colour is say a property of surfaces to reflect light at certain frequencies, then this is something that can be explained to a blind person. But when it comes to the experience itself, it may well be that someone who has not had any visual experience is not in a position to have the full concept of color that the sighted have, and so not in a position to understand the experience as fully as the sighted can.

Is there any evidence that colors are the result of micro-physical properties? That, for example, all blue things have a certain structure (texture?) in common that accounts for their being blue.

The answer to this may be yes and no. Yes, colors are or are caused by micro-properties of the surface of objects, but apparently quite different micro-structures may correspond to the same perceived color.