Here's a quick explanation of how I do my pictures.
So, from left to right:
-1: the lineart...basically, the sketch being inked, and some parts of it being thickened, to accentuate the dynamism of the pic.
-2: Plain colors are added. Nothing much to say here: I create one layer for each color --> it makes files a bit big, but permit to change every color easily.
-3: On another layer, I put solid shadows. Generally using that purple color, though I take a grey blue for parts that are in white.
-4: This what happens when I mix 2 and 3 together (3 being set on multiply). As you can see, the result is pretty good already.
-5: Here I work again on 2, this time shading the plain colors. Basically, drawing looks very soft after this.
-6: Mixing again, this time 5 and 3. Picture is almost done there. I also add another layer, where I put highlights (for eyes and hair generally).
-7: Drawing finished. I just worked a bit on levels and such...
From 1 to 7, it took me about 3 hours (2 hours if I wasn't distracted). I basically mixed a soft shading (the 5th step) with a hard one (the 3rd step).
I hope that tutorial (or rather explanation) of mine was easy enough to understand. ^_^