[R] Colors in a dendrogram

[Ayoub Maatallaoui]

Hello,
i'm trying to draw a dendrogram to show the clustering hierarchy. i'm 
working on 2 classes but each class contains more than 3000 instances.
i'm using the hclust function to do that! but i can't read anything from 
this figure.
i would like to color each class with its own color so at least i can 
extract some information from the clustering.
does any one of you did something like this before?

Regards,
Ayoub.