Pixel art is a great way to learn colour, but if you're struggling with perspective, lighting, and anatomy, then you should probably study those first using familiar, high-res medium. In pixel art, you will need to simplify and stylise these things due to the limited palettes and likely small sizes, and it's much easier to do that when you're already familiar with them.
Of course, you can always do both! It's likely you can already depict some things well enough to depict them in pixels without running into problems, and it might help you see where you need to focus your pen and paper studies. Learning a new medium doesn't have to come at the expense of another.
