why do colours fade in sunlight? specifically, what is it about light that has the ability to break down pigmentation? or perhaps, what is it about pigmentation that allows it to be broken down?
I think it’s generally oxidation that occurs, at least some chemical change of some of the molecules to ones having no color, resultant of ultraviolet energy from the sun, which has the right wavelength range to restructure the molecules.
Ray
http://www.straightdope.com/ubb/Forum3/HTML/001988.html
The thread was originally about bleaching, but someone asked about fading due to sunlight in there somewhere.
Basically: Ray’s right, it’s UV light.