Flags at sea. Before the days of radio, a complicated system of flag design and display grew up around the need for communication at sea. Flag codes enabled the sending of messages between ships or from ship to shore. A ship would salute another vessel by dipping , or lowering, its flag. Such salutes played a major role in international diplomacy.
Most national flags use one or more of only seven basic colors.
These colors are red, white, blue, green, yellow, black, and orange. Flag symbols often reflect historical events. The cross that appears in many European flags originated in the flags carried by Crusaders to the Holy Land. Some flags used in Arab nations show the eagle of Saladin, a Muslim warrior who fought the Crusaders in the 1100's. Burning is considered the most dignified way to destroy a flag that is no longer fit for display.