This is really nice. The characters are interesting, the standing poses aren't too static, and the coloring's pretty good. All in all I'd say nice job on presenting a cleaned up sketch. There's only one thing I'd suggest to help you with future sketches and pieces. Cropping. The first thing that anyone sees when they look at it this is a couple of characters drowning in a sea of white space. Although all of the attention is on them, the visual interest is reduced when the subject is out of sync with the canvas. A little composition and cropping go a long way.

yeah, I know.
It was late last night (~ 3:00 AM) when I finished and I was too sleepy to do anything other tha just post it as it was.