Baked Macaroni and Cheese Casserole

uncooked elbow macaroni 6 tablespoons butter, melted and cooled 1-1/2 cups milk 2 eggs 1/4 cup sour cream 1 teaspoon coarse salt 1/2 teaspoon white pepper 8 ounces Colby cheese, shredded 8 ounces white cheddar cheese, shredded