Color, but I always have a black filled layer set to color on top that I can toggle on/off to check values. I find that I basically repaint it if I try to add color to the b&w. Also, I grab colors, textures, details etc from photos a lot while I work so it just makes sense to go through the whole process open to adding/changing colors all along the way.
Thanks man! Material is flame resistant, but that doesn't mean it's made for running in fires, or that he does that. He's in areas that are hot, so he opts for short sleeves. If he gets caught on fire he'd probably wish he had a full suit, not just longer sleeves.