  Steingrimsson's coloring complex and Jonsson's unipolar complex are
interpreted in terms of hyperplane arrangements. This viewpoint leads to short
proofs that all coloring complexes and a large class of unipolar complexes have
convex ear decompositions. These convex ear decompositions impose strong new
restrictions on the chromatic polynomials of all finite graphs. Similar results
are obtained for characteristic polynomials of submatroids of type B_n
arrangements.
