If you hold the handles the sweat and oils on your hands can gradually discolour the handles and they start to darken and even worse become sticky. Its never happened to me because I am careful not to hold the handles in my hands (I hold it over my forearm instead) but I guess that seems kinda silly cause it is a bag after all
You can see lots of examples on ebay listings for used Bals. Its the first thing I check for - in photos the warming on handles can be a few to many shades darker then the actual colour of the bag.