Decorate cookies also 1 day in advance. Prepare royal icing following recipe directions. Tint portions of icing green, orange, pink and yellow. Prepare four bags with couplers and tinted icing.
For pink and yellow cookies, use tips 14 (pink icing) and 2 (yellow icing) to cover cookie with basketweave, piping lines 1/8 in. apart.
For green and yellow cookies, use tips 4 (green icing) and 3 (yellow icing) to cover cookie with basketweave, piping yellow lines diagonally 1/4 in. apart.
For four-color cookies, use tip 2 to pipe vertical rows of x's in alternating colors. Let all cookies dry 8-12 hours.