well it is designed to have a contrasting colour of that of the parent bone. Meaning if you have one bone which has a colour of blue and you create another bone, anim8or will choose a colour for the second bone's weight to something other than blue (something that will contrast it).
This done automatically on purpose I assume because if you chose bone #1 to be blue, and bone #2 to be blue as well, then you wouldn't be able to tell the difference of where the weight of each bone is.
P.S. Steve, if you read this, this took me about 30 minutes to post due to the connection issue again, just so you know.