Haha I like the little red signature. It's like those stamp things chinese calligraphers/artists use. But I think you should've put it somewhere on the grey-blue background, so it wouldn't have that black line through it.
When people kick, don't they stick their heel out more? Also, where's the rest of his right arm?
The coloring is very good. The colors are very consistent with the manga. Even though I linked here from the lineart version, my first reaction when I saw it was that you'd stolen it from a volume cover or something ^__^;
What do the characters on the bottom say? I know the middle one is wind, and I think the left one is demon?