@SoleneMa & @bengold - I saw a few examples of code to do this (and have used them myself) whilst developing ColourColor. I'll dig them out and get back to you.
EDIT: here's a solution by the guys at Panic. It's for Mac (based on the coloured cells in iTunes 11), but can easily be converted to iOS. If I find the other examples then I'll let you know.
http://www.panic.com/blog/itunes...
ReqRes
Adaptive Backgrounds
Call To Action
Lydia
Moleskine Studio