An interesting link: Why some see colours in numbers
Synaesthesia is "an extraordinary condition in which the five senses intermingle". It's like living inside an acid trip: numbers have colours, colours sound like music, words have taste.
I'm not fully synaesthetic, but I experience some of this. I see words and concepts in colour; Monday is pale blue, Thursday brown. The number five is blue too. There are words that fill my mouth with a disgusting taste when I say them, others taste like heaven (curiously, this happens to me more in Spanish, my mother tongue). It doesn't happen always, or with everything, but sometimes I can spend a whole day mentally rolling a word around in my tongue, enjoying the associations, until my brain gets sick of it. And sometimes I feel so overwhelmed by a sensory overload, reading poetry, looking at art or a landscape, or listening to music.
It's cool... but it also hinders my understanding of maths, since numbers are for me so loaded with associations (I tend to see letters instead of numbers, as well as colours and words) that it's very hard for me to grasp their abstract value.
Has anyone ever experienced this kind of thing?