It would be too hard to sand, remember that the layer of paint is only microns thick.
I haven't had a chance to try anything yet but I've been thinking about using a technique used to make metal badges, similar to the ones on this site - http://www.precision-badges.ie/
(no affiliation, just the first google result).
There's two ways they're done. With either method you'd etch your enclosure, sand, then paint the colour you want in the raised areas.
Use an enamel powder or paste to fill each recessed area in the colour needed. This needs to be baked to get the enamel to liquefy, flow out then cure.
Inject (literally, with a syringe and needle) ink into each recessed area. This would need to be a 2K/2 pot ink/paint - the layer would be too thick for a solvent paint to cure. You'd probably need to bake this also. A lot of experimentation needed here, getting the viscosity of the ink correct, correct needle size. Also as it's catalyst ink you'll need to work quickly to avoid the ink curing in the needle.
Unfortunately that's pretty much all I know at this point. I have no idea on the temperatures needed for baking enamel, materials cost etc, but may be a good starting point for if someone wants to look into it further. I'd imagine you'd need a pretty deep etch. It's a bit of a 'dying art' now so finding info and materials may be a little hard.