The painted notes (or tines) have no other function than to provide points of reference to the player, much in the same way as harp strings are coloured.  Without them, it is easy to lose where you are because one note looks very similar to the next.  It’s interesting that, for the most part, when you are learning you don’t ever think about this, but your brain is using the reference points – sort of “running in the background” without you being consciously aware.  Only when you play an unmarked instrument do you realise how much you rely on them.