  Given a set $S$ of positive integers, the integer distance graph for $S$ has
the set of integers as its vertex set, where two vertices are adjacent if and
only if the absolute value of their difference lies in $S$. In 2002, Zhu
completely determined the chromatic number of integer distance graphs when $S$
has cardinality $3$. Integer distance graphs can be defined equivalently as
Cayley graphs on the group of integers under addition. In a previous paper, the
authors develop general methods to approach the problem of finding chromatic
numbers of Cayley graphs on abelian groups. To each such graph one associates
an integer matrix. In some cases the chromatic number can be determined
directly from the matrix entries. In particular, the authors completely
determine the chromatic number whenever the matrix is of size $3\times 2$ --
precisely the size of the matrices associated to the graphs studied by Zhu. In
this paper, then, we demonstrate that Zhu's theorem can be recovered as a
special case of the authors' previous results.
