This is basically the same as a request I put in years ago, what I called "quality indicators". If you are working on several trees and they are getting quite large, it would be very useful to have some visual indicator to let you quickly determine the areas of the tree that still need work. I think colours would work fine for this, and should be optionally visible in any view where people are shown in a tree or list (for example the Index listing). It should be possible to turn this colour-encoding display on/off with a click of a button.
I would also suggest that the meaning of the colour codes should be user-definable, and that it should be possible to filter the Index list by colour.