This article contains three simple questions which I want to see answered. To organize the discussion, I'm creating a thread for each question, so people with an answer can state it or link to it. If you link, please provide a brief summary of your answer here as well.

First question: Where is color?

I see a red apple. The redness, I grant you, is not a property of the thing that grew on the tree, the object outside my skull. It's the sensation or perception of the apple which is red. However, I do insist that something is red. But if reality is nothing but particles in space, and empty space is not red, and the particles are not red, then what is? What is the red thing; where is the redness?