I definitely love your focus on clear and crisp shapes. I think you have an incredible effective way to inform about shape and posture on a glance, and I think the silhouette is strong enough, that you could even scale them down to very tiny depictions without losing any of that message (That is not meant as an actual suggestion for you to do, just as a mark of quality, that you could do it.)
At the moment you are basically using blue as a substitute for black, staying in a digital mode. And I must totally admit, that I can't tell you much about truely dipping into multi-color, as I have been postponing that step time after time.
I occassionally took a look into tutorials, and it's just a whole new can of worms compared to "simply" drawing,, with local colors modified by the color of reflected lights, decisions about saturation and using greyscales to harmonize color composition, new forms of contrasts, emotional "meaning" of individual colors or specific combinations of colors, deciding about a unified palette of colors for diverse effects.... maybe I shouldn't have looked so closely into all of the possible aspects, because now I am scared.
One name I remember from a guy who does great work with gouache and explains his thoughts while doing so was James Guerney on youtube.
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