You probably know these EL tee-shirts like this: http://www.t-qualizershirt.com/
Anyone know if you can buy the ink/paint somewhere and DIY?
I believe that (only took a brief glance) these t-shirts use simple led's. If you want to do something like this, I would start with RGB strips from Sparkfun. (about 16$ I think.)
The trickyest part is the powersupply though. Search in the excibit part of the arduino forum. There as a thread there where a guy did an ambient light for his laptop with one of these... you could make yourself a t-shirt using the same method. just cover the rgb leds with some diffuse material, like shower curtain liner....
Hope that helps.
See PUDDLEJUMPER project from http://www.aeolab.com