The Master Esthetician students at my school put on a presentation about fantasy make-up the other day.
I went to it, just for fun.
I learned a lot!
You can stretch fishnet or lace over skin then brush color on (or airbrush if you have such a tool) with the results looking like fish scales or rash. Using iridescent colors over a base color is a great way to make a fish scale look shine.
This was how the pattern on her cheek was made.