A business idea!

This is a machine to be placed in malls. The user chooses a color in an RGB color picker, and the machine mixes the colors and paints a plain white T-shirt with the color the client has selected.

I think it would be required for the client to wait a couple of hours - I don't think the making would be instantaneous. But he grabs a bite to eat at the food court, while his T-shirt is getting done. 

Why is this better than simply going to a store? You'd never find those colors there. The appeal is ultimate customization.