Cook macaroni according to package directions. Drain and set aside.
Melt butter in a large pot over medium heat.
Whisk in flour to create a roux and cook for 1 minute.
Gradually add milk, whisking constantly until smooth.
Add cheddar and Monterey Jack cheese, stirring until melted.
Season with garlic powder, onion powder, cayenne, salt, and pepper.
Stir in cooked pasta.
Heat through and serve immediately.
Garnish with fresh chives.