Seems it's something that if the user really wants, they can get it custom done at their own leisure.
Yeah they can, but there are risks and costs, where as if apple provided an option, that risk would be mitigated and hopefully the cost less then what colorware charges.
I've seen some of the work that colorware does and its quite striking. I'd love to see a black MBP but as I mentioned apple has moved away from color especially in their pro line up