Add 12 ounces Elbow macaroni and 4 cups of water to the Instant Pot. Close the lid and pressure cook on high for 4 minutes. Release pressure quickly and carefully, and drain the pasta. Set aside.
Press sauté on the Instant Pot. Swirl in the 4 tablespoons Butter in the pot, then whisk in the 1/4 cup All-purpose flour , to make a roux. Cook 1–2 minutes, stirring constantly to remove the taste of raw flour.
Gradually whisk in 2 cups Milk and 1/2 cup Heavy cream until smooth. Let it simmer for 2-3 minutes, or until it just begins to thicken.
Turn off sauté mode. Whisk in the 1 1/2 cups Cheddar cheese , 1 cup Colby cheese , and c4 ounces Cream cheese and continue to cook until melted and smooth. Season to taste with 1 teaspoon Salt, 1/2 teaspoon Black pepper and (if using) 1/2 teaspoon Paprika.
Return the cooked elbow macaroni to the instant pot. Toss to insure all of the pasta is covered in the creamy cheese.
To achieve a crispy topping, when the macaroni and cheese has finished baking, transfer it to an oven safe casserole dish, sprinkle the 1/2 cup Breadcrumbs over the top and broil in the oven for 3–5 minutes or until golden.