Thanks for the help!
It sounds soooo easy, but is somehow not so for now.
BUT, I know it
will seem easy after I finally hit all the right buttons in the right order,
understand how SP works (e.g. "fill layers are not paintable"), understand masks & UVs better, and practice it over & over.
Just takes time to learn a new app.

BTW, this is the latest try....I don't know how or what I did differently than the previous 10x,
but now the colors from the generator are working. Just need to adjust the size of the iris
to fit the eyeball.
Also,
this other thread is very helpful.
At some point, I'm sure it will all be clear, and I will say, "A-ha!"
