September 2006: It's a colorful country

In 1852 Francis Guthrie noticed that it was possible to color all of the counties in England using only four colors (with bordering counties having different colors), and he conjectured that every map could be colored using four or fewer colors. For over a century the so-called four color problem was one of the most popular and elusive unsolved problems in mathematics. It did not become a theorem until 1976 when Kenneth Appel and Wolfgang Haken proved it using a computer to check thousands of special cases. Even now there is no pencil-and-paper proof of the theorem.

By the four color theorem we know that it is possible to color the continental United States using four colors. In fact, it can be colored using four colors so that one color is used for only two states. What are those two states?

Here is a blank map of the U.S.

Dickinson College students can submit answers to Dave Richeson or Barry Tesman. You do not have to submit your coloring, only the names of the two states (there is more than one answer). The list of solvers will be posted at the end of the month.