Cook the macaroni according to the package instructions until al dente. Drain and set aside.
In a large skillet, cook the sausage over medium heat until browned. Drain any excess fat.
Add the bell peppers to the skillet and sauté until they are tender.
In a separate saucepan, melt the butter over medium heat. Whisk in the flour and continue to cook for 2-3 minutes, or until the mixture becomes a paste.
Gradually add the milk, whisking constantly, until the mixture comes to a simmer.
Reduce the heat to low and stir in the cheddar cheese and parmesan cheese, until the cheese is melted and the sauce is smooth. Season with salt and pepper to taste.
Add the cooked macaroni and sausage mixture to the cheese sauce and stir until combined.
Transfer the mac and cheese to a baking dish and bake at 350 degrees F for 20-25 minutes or until the top is golden brown and bubbly.
Let the mac and cheese cool for a few minutes before serving.