  We prove that the mixing time of the Glauber dynamics for random k-colorings
of the complete tree with branching factor b undergoes a phase transition at
$k=b(1+o_b(1))/\ln{b}$. Our main result shows nearly sharp bounds on the mixing
time of the dynamics on the complete tree with n vertices for $k=Cb/\ln{b}$
colors with constant C. For $C\geq1$ we prove the mixing time is
$O(n^{1+o_b(1)}\ln{n})$. On the other side, for $C<1$ the mixing time
experiences a slowing down; in particular, we prove it is
$O(n^{1/C+o_b(1)}\ln{n})$ and $\Omega(n^{1/C-o_b(1)})$. The critical point C=1
is interesting since it coincides (at least up to first order) with the
so-called reconstruction threshold which was recently established by Sly. The
reconstruction threshold has been of considerable interest recently since it
appears to have close connections to the efficiency of certain local
algorithms, and this work was inspired by our attempt to understand these
connections in this particular setting.
