For most of the fly patterns in the Effective Box, I try to have two sizes of each pattern in three colors. Maybe three color tones is more accurate. I usually tie a black and a tan or natural fly to hit either end of the spectrum. I find that olive is sufficiently buggy/fishy and slots in the middle between light and dark.
Limit your choices to these tones, but don’t feel bound by those colors. If a white wooly bugger works on your stream tie it. Experiment with mixing light and dark dubbings and come up with a Hare’s Ear nymph that kills on your stream.
Color is the cheapest and simplest thing you can change about your flies. Dark olive dubbing doesn’t cost any more than light green. All the different colors of a material also tie in the same. Barred tan marabou instead of black doesn’t require different technique. Mix it up, don’t cost ya’ nothing.