Okay, I just had my mind blown by discovering that using blending modes with
adjustment layers can give all sorts of bizarre effects. And another
explosion occurred when I started to paint with black on a Levels layer set
to Lighten mode and discovered that it could be made to darken areas painted
over.

Aside from long and protracted experimentation, is there anywhere to learn
about such complex topics? A book? A web site?

TIA
Norm