Starships have plenty of lights on them.
Your question ignores the fact that starships have their own lights on the exteriors of their hulls. In the images above and below (from The Motion Picture) you can see quite the contrast between dark and lit-up parts of the hull.
I would say that these images also answer your question of "How would a ship look to another ship in deep space where there is not much light?"
As a further example, here is a close-up of a Klingon Bird-of-Prey, showing running lights and contrasting regions of brightness and darkness:
