[igraph] Question on layout.drl .... What are the colors?

[Peter Flom]

Hello again

Sorry to be asking so many questions!

I have a connected component that I am trying to graph. When I run

plot(component1, layout = layout.drl, vertex.size = 1, vertex.label = NA,
edge.arrow.size = .1)

some of the links and nodes are blue, some are black. I didn't see anything
about this on the documentation for .drl, and the example they give there
shows up in all black.  Eventually, I will want to change the colors of the
nodes, but I am curious as to what is going on

Thanks!

Peter