Welcome to Gaia! ::

If you used more color in the rendering of the skin tone it might look more interesting. She also sort of stays one uniform color all over her body...try pushing some different tones/pigmentation on different body parts...an obvious one would be the knees..etc..

I personally don't think it's wrong to use white when rendering an image, but if you don't, then i wouldn't simply revert to gray. Try yellows, blues, greens or pinks. I think the idea behind the no white thing is that everything we see is composed of colors where as pure black white and maybe even grayscale don't exist because they're also made of colors.