Ive never used pastels for my winter scheme. I always airbrush on a coat of acrylic white over the original paint scheme (seal the paint scheme before applying the white). Once its applied I wait until I can handle the model. Maybe 20 minutes acrylics dry fast. Then , using a stiff brush of different sizes I take acrylic thinner and scrub away any areas that might see serious wear, i.e around edges , engine deck, turret top, around hatches etc....Its worked great for me. I usually use Tamiya white thinned to your liking.