well if it was the new penryn one, then of course. Apple doesn't paint the blackbooks anymore.
But were they ever painted? Not according to this, from July 2006 when the original black Core Duo MacBooks were still the newest ones:
Ok, had to know for sure, here is a nice deep cut inside the battery compartment inside my MacBook, as you can see it's black all the way through. Good news. Seems that brush scratching the matt black finish makes it look like a white scratch. Giving a light scratch a good hard rubb will make it black again.

http://www.flickr.com/photos/puckman/200237375/in/photostream/