Ohh I really like the blue one! If you think about when you link your sidekick to your hero the blue one should work well because the colour compliments your hero's hair colour but it'll also depend on her outfit because it should compliment that too so that they look like a team but shouldn't be too similar. :D
looking good, caplan america! i understand that the blue colouring compliments other aspects of your project, and that it fits the ghostly nature of the character, although my immediate impression was more sea creature than ghost. the purple and green seem to fit the bill a little more somewhat, nudging it away from the undersea beast and more towards jurassic specter, although the purple gives a more ghostly impression than the green, simply because green is kind of a primary colour when it comes to dinosaurs.