Roll refrigerated sugar cookie dough to an 1/8-inch thickness on a lightly floured surface; cut with a (3- x 5-inch) mitten cookie cutter, and place dough on parchment paper-lined baking sheets.
Bake cookies at 350 for 8 to 10 minutes or until edges are lightly browned. Cool cookies completely on wire racks.
Tint half of ready-to-spread vanilla frosting with blue food coloring gel to desired shade.
Spread frosting evenly on cookies.
Spoon remaining half of frosting into a 1-qt. zip-top plastic bag. (Do not seal.) Snip a tiny hole in 1 corner of bag, and pipe decorative designs on cookies.
