Yes, just pick a base colour that is slightly darker than white. I wouldn't use a flat grey, though - I usually try to take a bluish grey (either GW Space Wolves Grey or a a 30/70 mix of GW Shadow Grey and White). Personally, I don't drybrush much, even when Epic scale models are concerned - I usually take the base colour and then add two further layers on top - first the base mixed with white and finally pure white for the highlights.
Tried off a black base coat last night. I layer grey then heavy drybrush light grey, followed by drybrush white with line in with black .2 mm pen. Did not really want to have to do the line in but it really helps the look of the model.