I was sure I'd posted about synaesthesia before - but unless I've done it without tagging, I haven't. At least, Technorati thinks not. So here goes. I don't usually think about being a synaesthete, because I've never known what it was not to see colours, for example, related to numbers, letters or names. I used to argue about it with my mother, who saw different colours - it was normal, wasn't it, if we both did this? So 4 - as a figure or a word - is blue-grey; 5 is yellowy-orange, 9 more yellow. My own first name is pink; John is blue. Wednesday is a blue green, Tuesday pea-green. Get the picture?
And now Mr Heathbank has kindly sent me this link. In it, a neuroscientist links synaesthesia with metaphor, and states that what appears as metaphor is a literal sensory experience for synesthetes. That may explain, he said, why synesthesia is eight times more common among poets, artists and novelists than the general population.
He goes on to link the phenomenon to our ancestors' ability to climb trees - but I suggest you follow the link for that bit. I've just realised that McIntosh is a sort of deep russet colour, and doesn't go at all well with pink.
Update: I just completed a fairly lengthy online test for synaesthesia, which not only confirms my known associations but shows that my strongest manifestation of it is between colour and the sound of various musical instruments - here.
I'd never even thought about that one!