How do you perceive color? Because someone told you 'red' is red.
I don't think it's that farfetched to think someone told him what color things are, and that he organizes his paints in a way to use them. That's Blind 101.
Or maybe it's a big grand scheme. He's not REALLY blind, and he doesn't REALLY paint.
edit: at least no one cried
'shopped!