So I've been putting this off, but no more! Here are some guidelines to making acceptable pokemon:
1) Shinies are not permited. Shinies are rare and if we let everyone have one then they wouldn't be rare anymore.
2) Legendaries are not permited either. You saw this one coming though.
3) Your pokemon may have slight variations in desighn. This does not mean changing the pokemon's entire color scheme. The purpose is to make your character unique, not a rainbow. A good example would be: "Bob the pikachu has an odd black line following the inside of his tail. It zig-zags the same way the tail does."
As long as you follow those guidelines then your pokemon choice should be fine. ^^