Aw yeah, thanks for the kind words everyone!
Here I'm just documenting: this is the result of what I call the "exploration layer", where I just throw everything on one layer and see what sticks.
Color and light are an iterative discovery process, so you can't expect to land on the final color scheme without stumbling around. Here I just go with messy, bold strokes. I color adjust all the time. I try things. Eventually, after an hour or two of messing around, I've finished exploring because I'm happy with the state of the thing.
This is significantly faster than any greyscale --> color method, as well as any method that involves having light, shadow, highlights, etc. on separate layers. Trust yourself, paint under your line art on a single layer and make some decisions.
It's hard at first, but the payoff is that this method is also significantly more fun.
This is the last time I have to use my brain in the entire process - now I can shut it off and just clean up while watching some youtube video in the background. That's the easy, relaxing part!