We study Markov chains for randomly sampling k-colorings of a graph with maximum degree ∆. Our main result is a polynomial upper bound on the mixing time of the singlesite update chain known as the Glauber dynamics for planar graphs when k = Ω(∆/ log ∆). Our results can be partially extended to the more general case where the maximum eigenvalue of the adjacency matrix of the graph is at most ∆ 1− , for fixed > 0.The main challenge when k ≤ ∆ + 1 is the possibility of "frozen" vertices, that is, vertices for which only one color is possible, conditioned on the colors of its neighbors. Indeed, when ∆ = O(1), even a typical coloring can have a constant fraction of the vertices frozen. Our proofs rely on recent advances in techniques for bounding mixing time using "local uniformity" properties.