I think it depends on the machine and also the colour of the flipper bats. I also believe in keeping the colours the same as they were when the machine was manufactured, but I know that there is varying levels of "bounce" and maintenance associated with the different coloured rubbers so it is the owner's preference for the style of gameplay that they prefer. I will stick with the original black flipper rubbers on my Judge Dredd machine, I think it suits the "dark" theme of the playfield.
Matt