I was going to use the same color scheme as her coronation dress, but let's be honest. That thing was hideous. You could tell someone just chose colors they thought little girls would like. And hey, did you notice that her dress was the same colors as Cadance's coat and mane? I think someone's leaning on a poll result a little too hard...
Speaking of dresses, in this episode, the only ones that looked any good were the ones the other main five were wearing. The princess dresses were absolutely disgusting! At least, color-wise they were. They might have looked better if the colors actually complimented the manes. At first I thought Cadance's, Celestia's and Luna's were only hideous to make Twilight's even better by comparison. You know, like bride's maids' dresses; they're gross or plain to make the bride even more gorgeous. But no, Twilight's dress was just as bad. Lame. Lame. LAME.
It is my head-cannon that Rarity was not commissioned to make the princess' dresses this time around, so she just made dresses for herself and her friends that weren't being crowned. Otherwise, she is seriously losing her edge.
Anyway, I decided that pinks and yellows did not go well with the tone I was going for, nor her mane and coat. That, and her Element of Harmony and cutie marks blended in a little too much.