Check-out this really long blog post about a 4×4 rgb cube. Well detailed.
Normally I would probably have postponed making this thing, but then I spotted an arduino contest at instructibles.com. I thought I could have a chance. The deadline was november 15th I believe it was, so I had two weeks to complete it… Well, I completely blew that timeline I kind of suspected it as the deadline got closer. But then I had started, and I was actually progressing with this thing. So I continued making it even after the deadline had expired. I was kind of finished at mid-december, except I still had (and have) some programming left to do. I would also want to make a nicer physical finish on it some time, but for now this is what I’ve been able to do with what I have.