Given a graph
, its
-coloring graph has vertex set
given by the proper
-colorings
of the vertices of
with two
-colorings
adjacent if and only if they differ at exactly one vertex. Beier et al. (Discrete Math.339:8
(2016), 2100–2112) give various characterizations of coloring graphs, including finding
graphs which never arise as induced subgraphs of coloring graphs. These are called
forbidden subgraphs, and if no proper subgraph of a forbidden subgraph is forbidden,
it is called minimal forbidden. In this paper, we construct a finite collection of minimal
forbidden subgraphs that come from modifying theta graphs. We also construct an infinite
family of minimal forbidden subgraphs similar to the infinite family found by Beier et al.