I actually don't mind the idea of a more monochromatic colour scheme tbh. I can see how it'd work when the image is fully fleshed out. I think subtly altering the values so that it's more of a analogous colour scheme (I straight up had to google that y'all, I don't know art lingo), could maybe give a smidge more contrast without going full on complementary colour scheme. Not that there's anything wrong with that, it's just fun to break away from here and there.
Regardless, enjoying your progress. Look forward to more.