change individual label colours in a cluster plot?

I am doing some bibliometric analysis of interdisciplinarity using
cluster analysis of co-authorship.

I'd like to be able to specify the colour of individual authors in the
labels to show a prior grouping by discipline (red for sociology
authors, blue for economics authors, ..., that sort of thing).

Is there any way of doing this sort of thing? I'm hoping for something like:

h <- hclust(authors.dist)

h$labels <- colorlabels(c("red", "blue",..., "green"))

plot(h)