Would you like a Mac that could change color? Probably won't happen, but Apple has considered the idea. In 2003, Apple filed a patent (number 20020190975) for just such technology.
It involves "electronic devices that are capable of dynamically changing their ornamental or decorative housing." Besides looking cool, imagine a Mac that would change colors to alert to specific things. Say, it turns red when you have new email, blue when the latest system updates are installed, etc.
Here's Apple's summary of the patent (invented by Duncan Kerr): "The electronic devices generally include an illuminable housing. The illuminable housing, which includes at least one wall configured for the passage of light, is configured to enclose, cover and protect a light arrangement as well as functional components of the electronic device."
Apple says the advantage of a color-changing Mac would be that it could provide additional feedback. How so? Here's one example that Apple gives in the patent filing: "External lights have been used in some devices associated with displaying video to enhance the viewing experience of the video. Unfortunately, however, none of the external lights have been capable of changing the ornamental appearance of the device housing. That is, the external lights are typically located outside the periphery of the housing and are typically arranged to alter the environment in which the video is shown rather than the device housing itself (the appearance of the housing remains the same even with the use of lights).”