Make a roux by melting butter, add flour and stir, then cook over low heat for 2 to 3 minutes while stirring constantly. Set aside to cool.
Cook macaroni according to package directions. Drain and put into a disposable foil pan.
While macaroni is cooking, heat 8 cups of the milk, add the Colby and Cheddar cheeses and cook over medium heat while stirring to melt cheese.
Add the salt and white pepper to the cheese mixture. Add the roux and stir until well thickened. Add this cheese sauce to the cooked macaroni and mix well to coat macaroni. Pour in the remaining 2 cups milk.
Combine the bread or cracker crumbs with the melted butter and sprinkle over the top of the macaroni. You may prepare it this far, refrigerate, and bake it later.
Bake at 350 degrees F for about 30-45 minutes or until bubbly in the middle.