Microwave vanilla frosting in a bowl until slightly runny; transfer some frosting into 2 or more smaller bowls; color.

Add small amounts of colored frosting into remaining white frosting and swirl.

Dip cookie face down into bowl of swirled frosting.

Let dry completly on a cooling rack.

Frost design onto cookie.

Dip cookie face down into a shallow bowl full of sprinkles.

Fill muffin tins with different colors of frosting.

Use a clean brush to paint frosting onto cookies.