Answering this question is always difficult, because I feel like I need to like. Physically show how I do it with commentary or something lol. I have a light gray layer as my paper layer. Then, on a transparent layer on top of that one set to multiply, I paint with a single dark color and an eraser in washes. Anything darker than the paper color below is just various opacities of the same color, and the brightest parts are literally just the paper layer below showing.

So when it comes time to actually color, I lock the multiply layer and start throwing down the general idea of what colors I think I want. Sometimes I use photos that give me that specific mood, blur them to hell and back, and build up from there. But because I'm throwing color on the layer beneath the transparent painting, and then color on the locked multiply layer, it gives me some interesting effects that I think throwing color down on a fully opaque black and white painting wouldn't give me. And when I'm happy with that, I make a new layer of everything merged down and then I just. Paint. Aside from the initial two layers, I paint on a single layer the rest of the time. Duplicated a bunch at various stages, but that layer I actively work on is always a single one.