Hi Stan first off what vehicle and is it whitewashed.also is it a frozen russian winter or during the thaw.reason is if the ground is frozen you wont get no mud but churned up dirty snow.to weather the whitewash you could give it a burnt umber wash more thinner than paint that will get a grimy look ,try dry brushing with your base colours along edges and some scratches with the base colour.i would reccomend you surf this sight theres plent of winter schemes which will give you plenty of Ideas.all the best.