Perceptual shifts may also be medical, as in synaesthesia.

NLP practitioners have shown that they can pretty easily induce synaesthetic color experiences in most anyone, indicating that the experience is not actually rare at all -- only the recognition of it is.

As mentioned in this Science News article, researchers have found that color expectations can have direct effect on readability of (Chinese) text -- seeing the word "red" written in blue takes longer for the brain to process and understand.

"The psychology comes from the underpainting" is one of the strangest lines I've read in weeks.