What a bizarre thing to say... I've always been fascinated by synesthesia, as someone who doesn't have it, partly because it's one of the...hmm, not disorders, but abnormal mental wirings...that doesn't seem to have a downside! People with it don't want to be 'cured', except for occasionally being surprised that not everyone sees like they do there's no different functioning. I suppose I kind of thought that was common knowledge.

If I ever take mind altering drugs (beyond alcohol and caffeine), it would be hallucinogens to try to replicate synesthesia. Unlikely, but it's the only thing about the whole gamut of 'recreational' chemicals that's even vaguely tempting.

Also, you could write an amazingly Through the Looking Glass type story if you wrote it like that "Purple was last month, it's right over THERE" line WITHOUT explaining about the synesthesia first. :)