The only additional parameter related to vertex.colour is vertex.colour.palette.
It supports a vector of RGB or named colours (see colours for all named colours in R).
It also accepts complete calls to functions that return a such a vector like RColorBrewer::brewer.pal(n, name) or viridisLite::viridis(n, option).
If the palette is too short, it will be extended automatically using colorRampPalette.
If the palette is not declared, but this arguemnt is TRUE, it will defaulr to the following vector of colours:
If the argument is FALSE, NULL or NA, the vertex will be coloured of #081677 (Gentian blue).