The chromatic number is the smallest number of colors necessary to color the vertices of a graph or the regions of a surface such that no two adjacent vertices or regions are the same color.

Betti number | bicolorable graph | Brelaz's heuristic algorithm | Brooks' theorem | chromatic invariant | chromatic polynomial | edge chromatic number | edge coloring | Euler characteristic | fractional chromatic number | genus | Heawood conjecture | k-chromatic graph | k-colorable graph | map coloring | perfect graph | three-colorable graph | torus coloring

college level