If you want to know what they're going to look like in colour, check out these guys:
http://www.colorwarepc.com/content.aspx?id=20
They've been painting powerbooks for years. I have to say some of them look nice but they charge a lot more just for the paint job. I'd never buy one myself, brushed-aluminium is cool enough for me. But it makes for pretty pictures

They still sell only the G4's though.
Of course, these are powerbooks, and not macbooks, but I'd say they would look roughly the same in the new widescreen form factor.
Edit: The price difference wasn't as great as I said first, sorry.