Dry brush color for white base

My technique is to paint everything black, no matter what the color is going to be. That's my shadow.

Then I go and lay in the color (spray), leaving the appropriate shadowy areas darker.

If it's a dark color I'll add highlights by drybrushing with lighter shades of the base color and re-justify any lost shadows with either washes or pastels.

If it's a light color, the highlights are already there and there's usually little need for drybrushing, depending on the actual color. I'll simply enhance the shadows with washes or pastels and add additional highlights, only if necessary, again, with a lighter shade of the base color.


Fade to Black...

Also, you can start you color with a very light gray, such as Vietnam era underside camo gray. Give in an approproaie wash and drybrush with white.

Any surface that has depth or relief, even if white, is going to produce shadows and highlights. I would give the area a weak wash of either Sepia or black-brown, followed by a light dry-brushing with titanium white oil paint. If the overall effect appears too stark, you can always tone it down with light colored or light gray pastel chalk. But make sure the oil paint is bone dry before using the pastels.

If your base coat is pure gloss white, there's not much you can do. If its flat white, you can dry brush gloss white or Future. Another solution is to paint the base coat slightly off-white (add a MINUTE amount of black or pure gray to the white - you don't want to turn it gray, just alter the value of the white slightly). It will still look white, but the dry brushed white will be lighter. Just an idea.
Hope you find something that works for you.