depending on the type of paint you're using (acrylic, enamel) various companies make a 'chipping solution' that could be used. I know MIG and Vallejo make them. You would underpaint in your camo, apply the chipping in some areas (to show white wash washing away) and paint a very light, thin white coat. Then remove your chipping to show a more natural white wash. Instead of the 'chipping solution', you could google the 'hairspray technique'. I've never used this method, though I'm sure others here have, and I'm sure there's a good google video on it. The hairspray just being a cheap 'chipping solution'.
This is all assuming you want to have the white wash 'fading away'.