Outline and flow in cookies 1 day in advance.Prepare Color Flow icing following recipe directions. Tint portions blue, yellow, black, gray (use black icing color) and red. Reserve a portion white.
Use tip 3 and full-strength Color Flow icing to outline gray face; black engine, smokestack and undercarriage; blue cab; and yellow windows. Let dry 1 hour.
Use thinned icing in cut disposable bags to flow in outlined areas. Let dry 24 hours. Reserve remaining icing.