chromatic numberThe smallest number of colours necessary to colour the nodes of a {graph} so that no two adjacent nodes have the same colour. See also: {four colour map theorem}. {Graph Theory Lessons (http://www.utc.edu/~cpmawata/petersen/lesson8.htm)}. {Eric Weisstein's World Of Mathematics (http://mathworld.wolfram.com/ChromaticNumber.html)}. {The Geometry Center (http://www.geom.umn.edu/~zarembe/grapht1.html)}. (2000-03-18)