  A mixed graph is, informally, an object obtained from a simple undirected
graph by choosing an orientation for a subset of its edges. A mixed graph is
$(m, n)$-coloured if each edge is assigned one of $m \geq 0$ colours, and each
arc is assigned one of $n \geq 0$ colours. Oriented graphs are $(0,
1)$-coloured mixed graphs, and 2-edge-coloured graphs are $(2, 0)$-coloured
mixed graphs. We show that results of Sopena for vertex colourings of oriented
graphs, and of Kostochka, Sopena and Zhu for vertex colourings oriented graphs
and 2-edge-coloured graphs, are special cases of results about vertex
colourings of $(m, n)$-coloured mixed graphs. Both of these can be regarded as
a version of Brooks' Theorem.
