I belong to the French Association for AstroImage Processing (AIP). We just received notice of a new 4-page technical article on using the L-RVB (L-RGB) script in PI. Probably worth joining just to get the keys to this castle. It is in Astronomie magazine (No 167). Some of the info in this may be self-evident to experienced PI users, but I found it helpful. Also there is a basic L-RGB workflow (a simple 30 steps) that includes specific about blackening background in linear mode, which I found interesting.