Heat oven to 350ºF. Cook and drain pasta as directed on package.
While pasta is cooking, melt butter in 3-quart saucepan over low heat. Cook garlic in butter 30 seconds, stirring frequently. Stir in flour and salt. Cook over medium heat, stirring constantly, until mixture is smooth and bubbly. Gradually stir in milk. Heat to boiling, stirring constantly. Boil and stir 1 minute. Stir in mustard and Colby cheese. Cook, stirring occasionally, until cheese is melted.
Stir pasta and ham into cheese sauce. Pour into ungreased 2-quart casserole. Sprinkle with Parmesan cheese.