Stellar [stel-er] (adjective) -
1. of or pertaining to the stars; consisting of stars.
2. like a star, as in brilliance, shape, etc.
I decided to not do each individual color on her mane and tail with a different galaxy/nebula because I feel it would look too cluttered and messy. Using one "rainbow" colored nebula (Bello Nebula) looks far more appealing.
I also decided to not include the cutie mark because of similar reasons such as clutter and just my inability to make it look good. Aaaaaaaaand now Rainbow's colors are more emphasized and really pop and draw your attention (in my opinion of course).
's "Rainbow Dash 2" Vector [link]