I really like the sense of motion in this! It has a light and fun feel to it and I like your choices of colors, they aren't too bright and glaring but keep the mood of the pic light.
I'm guessing you didnt use layers for this. If not you ought to look up how they work, they will make your life so much easier I notice there are lots of white spots in the background next to Harry; to avoid this, change the layer with the sketch to multiply and add colors to lower layers. The black lineart will stay on top. There are lots of other ways to separate the black from the white, but especially for newer digital artists this is probably the easiest
Okay thank you so much. I'm still really new to using GIMP, for the longest time I just did minor coloring and such on picnik.com, and I find the GIMP user manual very tedious to read so I only really read that when I'm in need of help, therefore I haven't gotten very far through it yet...heheh I just don't have the attention span to read and understand most of it.
Thank you so much again, your a big help