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'.