Something of an abstract from my friend's diploma work on perfect pitch (he has p.p.):
Perfect pitch is a matter of neural connections in the brain: All newborns have perfect pitch, but as a person grows older, the number of the connections decreases and the ones that relate to perfect pitch are usually lost before two years of age. However, if the brain is subjected to enough music at this early age, the critical connections may not be lost and therefore the perfect pitch is preserved. However, it has proved to be impossible to acquire perfect pitch after it has been lost. [...] A substitute can be developed, though - people can for example recognize if their favorite piece has been transposed or not, if they have listened to the original version enough times. However, this is pure memory, which has gotten sensitive enough to even such a subtle change as transposition - the brain is just comparing what it hears to what it has heard sometime in the past. [...] As to the color method: yes, some great musicians of the past (Scriabin...) described their perfect pitch as frequencies associated with colors, specifically as connected to the "fifths circle".
Dunno. But I tend to take this rather sceptical standpoint...