To be honest,
There's not enough color in this picture.
It's plain and neutral.
You could have played a little with this picture.
Mostly with shading, detailing and background.
Though, this picture is cute and has a little place in the Fionna fans,
I think this should become more of what Fionna is;
Tomboyish and an adventurer.I understand that you were just coloring in, but atleast try to have some fun in the detail.
Though, I would like to say thank you for making this picture.
I may say it is simple, but you really made a big accomplishment in the Fionna fan community.