I'm pretty sure the stars have something to do with the difficulty/rarity of whatever you're fighting, but I'd like some more detail to it than the base knowledge I learned through trial.

What are all the different meanings of the colors?

I made a picture guide for some features of Sylestia, including the stars. c:

Number of stars denote difficulty.
Colors denote rarity (only applies to sylesti pets).
More detailed in the guide. xD

edit: I know it's kinda small; it was resized. ;_; I'll edit it to make it bigger when I have time.

Thanks!