Synesthesia is a mental phenomenon in which different senses (sight, sound, smell, and so on) become associated in unusual ways. A friend of mine has a form of synesthesia in which numbers have particular colors. I think it came out for the first time when she said my phone number was very blue and black. I asked her what she meant, and she explained how each number has a specific color, although these colors can sometimes change based on a number's proximity to other numbers. She also said that numbers and the fingers of her hands have particular genders. (Oliver Sacks has written extensively about these and other types of synesthesia, most recently in his book on music and the mind, Musicophilia.)
Perhaps my friend would understand Guitarati, a music recommendation site that launched earlier this week. The front page consists of a collection of colored dots. Click on a dot, and you will see some songs that somebody (editors at the site? the artists?) have decided fit into that particular color scheme. Users can sample the songs and, if they like them, stream them for a penny or download them for a price set by the artist (most songs are $0.99 today). Over time, as users listen to particular songs, they can vote on the color they should be, and the song's color will reflect the average of all votes.
I give Guitarati points for uniqueness, but I'm not sure I get it. OK, perhaps Brian El's song "Aquatica," which appears about halfway down the page for a blue dot, is kind of turquoise, but that seems to be a suggestion from the title rather than the music. Most of the other songs on this page don't seem particularly blue to me...in fact, the top song on the page, "Eddy" by Happy Elf, sounds too aggressive to be blue. Perhaps it's more orange. Then again, maybe I'm a bad test case--Kind of Blue has always sounded grey and black to me. More like a rainy evening, not a clear sunny morning.