Numberphile: The Four Color Map Theorem

Did you notice that maps use just but a few colors, while we have more than 200 countries here on Earth. Obviously it would not be rational to use different color per each different country. It is more convenient for our human vision, then there is as few colors as possible as then we can pick contrasting colors. Wouldn't it be interesting to know if there is some minimal number of differing colors necessary to create colored maps? More about this in this Numberphile video.