Here's a bit of a disclaimer. I'm not an expert at color but I am definitely finding that the differnce between an amateur painting and a more professional one must definitely include attention to details like color. Now to the point... I don't like using black. I don't see the color in nature very much and so when I use black in a painting, it looks un-natural. It's like a shortcut color to get a dark value effect on a painting. But I think it's a bit too much of a shortcut, especially for landscapes. Even the night sky is not really true black but perhaps more of a very dark blue + brown. Paintings with deep blues and deep browns feel richer and more interesting to me. That said, I don't doubt the power of grays. It think a master painter will typically be a master of using gray. It provides those subtle variations that really are in nature but are difficult to observe.