I'm frankly tired that it is such an important issue wether things are pixel or not.
EDIT: saw your sketches.
hm. I think the character transformed a little with the coloring process. for example the hair in the sketch makes me think of DBZ, while the colored guy has a little of Elvis hair in there.His face is better balanced in the painted over pic, and is a lot,lot rounder, looks a lot less anime but in this case I think it's a good thing.
were you aware you made all this changes? was it intentional?
I think you're off in a good start, there's good sense of volume, I like the way you darkened the teeth, there's conscience of the different hues that can be used to shade things, that blue tint looks good and the smile is well emphasized with the shadows you added.The scarf....or whatever that garment above his shoulders also has interesting hues.
there is some shy stabs at actual pixel by pixel work, with the eyes, with the ocasional linework at the eyebrows, fist and ears to help diferentiate things.
you defintively could use some work in GraphicsGale or Promotion to better understand shading though, it seems as if you rely on the airbrush/paintbrush tool of photoshop to create the depth, this is specially visible in the shirt which has a lot of random brushings that dont really say much, and the fist which has a lot of unclean pixels lingering around.
What do you want to learn pixelart for? do you want to animate? make tiles? perhaps portraits?