well with snow, you dont really need a mud colored base. When I did my bulge dio I used Plater of Paris. It dried white and then I covered it with the snow. If you want to have more shallow snow ( my dio was showing fresh powder it a storm) then use celluclay. Cover it in a dark brown color (because the ground would be wet it would be dark brown) and spread where desired. Then just put the snow where you want.
For making mud with the celluclay, you just need to color it and give it a coat of future. You can also make puddles with the future.
heres a pic of how my "fresh powder" worked out.
