Regular Colorings in Regular Graphs

An (r − 1, 1)-coloring of an r-regular graph G is an edge coloring (with arbitrarily many colors) such that each vertex is incident to r − 1 edges of one color and 1 edge of a different color. In this paper, we completely characterize all 4-regular pseudographs (graphs that may contain parallel edges and loops) which do not have a (3, 1)-coloring. Also, for each r ≥ 6 we construct graphs that are not (r −1, 1)-colorable and, more generally, are not (r − t, t)-colorable for small t.