Is color real, or is it only in the brain?

Color is real, and it belongs to the observer that reads it. Physics describes light by its wavelength, and surfaces reflect some wavelengths more than others. That pattern is a public fact, recorded by instruments and checkable by anyone. Redness is something else. In OPH it is a distinction an experiencing observer reads on its own state when such light arrives, and the reading steers what it notices and does next. That self-reading is as real as any public record, judged by the same standard, and it is private by construction, since public comparison keeps only what every party can check. The wavelength belongs to the shared world, and the redness belongs to the observer. Which colors a creature can tell apart depends on its eyes and on how its self-reading is organized, and the details are questions for biology. A bee and a person looking at the same flower read different distinctions on themselves.

Also in Chapter 11: What Does Everybody Actually End Up Holding?.