I know, it's too big a word for this time of night but I just found this post and it has enlightened me a great deal; specifically about my mother but also, to a lesser degree, myself.
Basically, "synesthesia is where a person’s brain gets sort of cross-wired and they see numbers in colour, or hear musical notes as numbers, or letters of the alphabet as colours, or sometimes sound." Apparently a lot of people have it and aren't aware that others don't.
I have often thought my mother was going loopy when she would make comments about what colour a particular sensation was or what sounds a painting made. I understand a lot more now.
I still think she's 'different' but now I'm less likely to try to have her committed!