That is SOP on the colors so that the crew knows what colors to spray automatically by the system and to reduce mistakes. What seems simple to a person on one change might be a nightmare to the production staff or prep staff as the cowls are gelled, laminated, pulled, fit in boxing, go to finish stage one for trim installation, then end up in finish stage two for the install during checkout. So just a set of cowl covers get handled by six different peole and systems are required to prevent mistakes. Decal colors are an example as they place them based upon an established protocol.