i use substance designer a lot (a program for making textures procedurally) and one of my favorite features is "pick gradient": you click that, drag across an image open on your other screen, and it'll record a list of the colors and apply that to your grayscale input.
in short, it slurps colors off any image and makes the things you made look colored similarly.
so what I do is going to google maps, find a particularly nasty sludge pool, and sample its colors. there's so many cool color palettes to be found there!
