Well, maybe the dark color is indicative of some sort of detection-resistant coating, similar to our modern-day stealth aircraft.
Stealth in space--[near magical] Klingon/Romulan cloaking device aside--would be damn near impossible. Unless you had a way of shielding thermal and EM changes (just off the top of my head, the warp core along has to bleed off a lot of exotic radiation types) in the local area, a ship would stick out like a sore thumb. Granted, distance is your friend, further out you are from the observer, the better the chance that you could bleed into the cosmic background noise. But in the close up fistfights we see as the norm in Trek, forget about it.