Content distribution and nested groups

How would I do the following on a WPMU/BuddyPress site using the MU theme?
Create the following groups and sub-groups:
Red Group
Red Riders sub-group
Red Runners sub-group
Red Walkers sub-group
White Group
White Beads sub-group
White Bracelets sub-group
Blue Group
Blue Shirts sub-group
Blue Pants sub-group

As a moderator of the Red Group I know that if I create a post or write a message it will go to all members of the red group. What I'd like is the ability to send a post or message and be able to select which of the nested groups receive the it. So if I'm the moderator of the Blue group and I create a post or message specifically for the blue pants how can I keep members of the blue shirts from seeing the message? Is there a plugin to manage this?

Any responses appreciated