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.
The primary Biblical reason to fast is to develop a closer walk with God. By taking our eyes off the things of this world, we can focus better on Christ. When you fast, do not look somber as the hypocrites do, for they disfigure their faces to show men they are fasting.