I want to make a spell that will increase my characters ability and change his skin color. I would also like to put a mark on his face but I can learn about that later. Is it possible to make a spell that will change my color?

Possibly, by making a magic effect shader and applying it to him (with the skin only tag set if you want that). However, other effect shaders might interfere with it.

I need a step by step or a link to a tutorial because the only thing ive ever made is a custom summon.