[Fateful_Ikkou]

Personally I wouldn't but If I were to paint it I would use a High heat resistant spray paint so you can evenly coat it but remember when spray painting do passive sprays (Like how you Strafe when gaming) and don't spray too much in one area even with small objects like a heatsink because if you do too much heat may get trapped in that area, effectively reducing your heatsinks capabilities.

Good luck with your project.

And like rheicel said "One coat should do just fine"