Ugh, shading white. I'm learning, but I see how you managed to pull that off. Good job!

Haha, in the words of Bob Ross, "pure white is disturbing."
I typically start with a slightly off white or light gray and shade with a little bit of color (depending on what the surrounding colors are, though a dull blue will get you a decent result most times. )
After that, you can highlight with a pure white and mix it in a bit so it doesn't look so unnatural.

I seem to have lost my favorite color theory quick tutorial, but doing a little bit of research on that helped me a TON when it came to coloring and shading.

Thank you very much for the compliment, and I hope this helps!

Hm, getting a lot of blue/purples suggest when it comes to shading!
That's a good way to go around it. But the product above already says enough. ^^