i'm not sure why you are using white and black in that fashion but everything just ends up sort of a whitish gray color with some black ^^ you need to use the white sparingly, esp the white whites which will be for the brightest of highlights. you may want to try the opposite approach which is to put in darks on lights, maybe get some lineart and color it in. are you using a tablet?
anyways i think maybe you should hold off on complicated subjects on the computer until you get better at handling the medium. they don't match the quality of your traditional sketches at all.