How to color dendrogram according to the class of the objects and not according to the cluster membership?

I am creating a dendrogram containg 30 obejects: 10 belongs to class B, 10 to class R and 10 to class G.

I would like to have the dendrogram colored accoridng to the class, i.e. Blue for class B, red for class R and green for class G, irrespective from which cluster they belong.

I have played around with the various options from the dendrogram function.

Any clue on how to solve this problem?

Thanks Edo