Like notaries, witnesses aren't generally required in order for a contract to be legally enforceable. However, each state may require special kinds of contracts (e.g., real estate deals, wills, and marriage agreements) to be witnessed by a third party in order to be binding.
McDonald's, apparently, use red and yellow because red=fast and yellow=hunger (hence fast food!). Remember also that meaning is what we create. It does not exist in the color itself and individual meanings may or may not exist in different cultures and individuals.
This color is also commonly associated with energy, so you can use it when promoting energy drinks, games, cars, items related to sports and high physical activity. Light red represents joy, sexuality, passion, sensitivity, and love. Pink signifies romance, love, and friendship.