Mr.Bionic: There is NO rule in golf that says you have to play the same COLOR ball, just the SAME type.
This came up before on the forums, and the way it works is that there is a USGA list of golf balls from all producers and in fact it lists different colors as being different types of balls. Absurd, really, particularly as here they are only virtual balls. The requirement to play a single type of ball over a stipulated round is optional. On the other hand, if players were allowed to change balls between holes there would be no end of it.