  Let $P=B\cup R$ be a set of $2n$ points in general position, where $B$ is a
set of $n$ blue points and $R$ a set of $n$ red points. A \emph{$BR$-matching}
is a plane geometric perfect matching on $P$ such that each edge has one red
endpoint and one blue endpoint. Two $BR$-matchings are compatible if their
union is also plane.
  The \emph{transformation graph of $BR$-matchings} contains one node for each
$BR$-matching and an edge joining two such nodes if and only if the
corresponding two $BR$-matchings are compatible. In SoCG 2013 it has been shown
by Aloupis, Barba, Langerman, and Souvaine that this transformation graph is
always connected, but its diameter remained an open question. In this paper we
provide an alternative proof for the connectivity of the transformation graph
and prove an upper bound of $2n$ for its diameter, which is asymptotically
tight.
