In large bowl, combine margarine, sugar, egg, milk and vanilla; mix until light and fluffy. Lightly spoon flour into measuring cup; level off. In medium bowl, combine flour, baking soda and salt. Add flour mixture to margarine mixture; mix well. Place half of dough in plastic bag or wrap in plastic wrap. To remaining half of dough, add peppermint extract and red food color; mix well. Place in plastic bag or wrap. Refrigerate both portions 1 hour.