spray paint would be cheap and nobody is going to get so close they could tell the difference. I would go with black as the white would be hard to match with the case.
I've done the top of the Hyper 212 EVO coolers but not a I/O should be easy just do it and let it dry might hit it with a blow dryer or heat lamp for a bit to help it cure.
The main thing would be keeping it from cracking if it flexes when installing it a bit of clear coat should help that you can also buy that in spray.