Ohh, it's a toss up between Colette and Violette. Both very creative! I know a Letty once, I am pretty sure it was short for Letitia. I wish I could like Letitia, but cannot stand it. Letizia is a touch better and less lettuce-like.
Well, I knew a Letty once. It was short for Leticia. So Letitia / Leticia is what neturally comes to mind for me first. Letitia, Colette or Violette are my favorites from your list. Since it's a character and you can really have some fun, I vote Violette / Violetta. Final answer. :-)