Zero and Yuuki - Coloured Pencil Drawing

Hi there! It has been a long time that I've colored a drawing.. 4 years or so?
Okay, I wanted to color this sketch for a test... I wanted to test some cheap coloured pencils. So this is how it turned out!
I've edited the background black.

I used an outline, because I thought the pencils doesn't work well and I would ruin my sketch.
I used the outline of someone, but I can't find his outline anywhere :S

I hope you have some advise for me, that will really work for me. I'v didn't colour for years ._.