Heat oven to 350 degrees. Boil salted water for macaroni. Cook until under al dente, about 4 minutes. Drain and rinse under cold water. Set aside.
STEP 2
In a large bowl, whisk milk and eggs. Stir in macaroni, 2 cups cheese, melted butter, salt, and pepper. Mix well.
STEP 3
In a baking dish, layer half of the macaroni mix. Sprinkle 1.5 cups Colby Jack on top, then add the remaining macaroni mix. Cover with foil and bake for 30 minutes.
STEP 4
Remove foil. Top with 2 cups Cheddar and 1/2 cup Colby Jack. Broil until cheese browns, about 3 to 5 minutes.