The colors go great together. Nice find! ouo

Looks great!
First things first, the best thing you can do is go online and search Pony Tutorial/Pony ananitmy guide. Theres tons of people who expain things better then I can, but I'll give my two bits.

The colors on the main are a little loud(bright) and clash a bit. The head is a bit big compared to the body, you want the chest and torso to be the same size of the head.
Shorten the waist so the legs are closer, maybe ad a bit of thinkness to them also.
No really background, but make sure to not use similar colors to the pony or it will blend in.

Keep it up! Your art is great!

Also I think theres a tag for new pony artist

#PonyArtistsUnite

finished (: