Here’s a neat concept idea by Jinsun Park, a physical Color Picker. It is kind of like the color picker tool in a paint program, except for physical objects. Though the design won’t work as proposed (for starts, you would need CMYK ink in the pen to be able to draw), it seems like the optical scanner part could be made to work. I think all you would need is a white light source (maybe a selection of different LEDs?) and either a color light sensor or some photocells with light gels on them. Think it would work? Have you already made one? [via core77]
Update: As an anonymous commenter points out, the Sparkfun module I linked to already contains an LED, so you could just use it as-is. If you want to make your own, check out this project.