It's a year later, but I'm finally using this with Jaymer's help.
Very slick feature!
Nice to be able to set Presentation Rules on an attribute with one simple step. For example, on Category.Name attribute Presentation Rule:
background: <<Category.Color>>
Then by turning on "Use style defined ..."

the Category.Color picked in an instance of Category BO is used as the background color for Category.Name
That Color can then be used as Category is assigned to instances of Orders related to a particular Category.