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 is the color with the longest wavelength, and is the nearest visible light to infrared in the electromagnetic spectrum. The color red stands for enthusiasm, passion, anger, energy and security. It educes extreme emotions in people and being a color of passion can lead to hostility, violence and warfare.