If you are lucky enough to find a spare ball mech they are easy to repaint. I did that years back for my BaB. I remember I needed a 1 ball. bought a can of Krylon Short Cuts (like $3) sprayed it yellow then replaced the number.
re: Balls Breaking -- they also can break off when they reset at the start of a game when the large coil slams them back -- if they are not tightened all the way up. As others have mentioned the wing nuts are the key -- they have to be TIGHT at both ends and work loose over time due to vibration etc from play. I routinely retighten mine if I'm in the backbox. Preventative maintenance is the key.
