Instead of using a decorating bag and tip, place the frosting in a resealable food-storage plastic bag, cut a tiny hole in one corner and use to pipe the frosting. Use different bags for different colors.
Look for paste or gel food color in cake decorating departments of craft stores.
Create an attractive display by covering a piece of sturdy cardboard with wrapping paper; then plastic food wrap. Stretch and secure with tape. Or cover cardboard with foil or cooking parchment paper.