An internal light device can be configured with any settings of red, green and blue to display any color. Although there are no concrete plans as yet to introduce this immediately, its a good bet that this will wind up being a feature of the next generation Mac.
Personally, I welcome anything that moves the computer away from being an ugly grey box. With computers becoming more and more interlinked with our lives, they are popping up all over the home, and there needs to be provision for them to blend in as currently TVs, videos and HI-FIs can do. It would certainly be a fine thing to be able to make your computer match the wallpaper or carpet that you have chosen.