TheLighterDark:
While it is against USGA Rules [I believe] to replace your current ball with a different type of ball, it is not against the rules to change colors. This is something that you will have to deal with.
It is actually legal acording to the USGA Rules to switch balls during a round, as long as it's at a correct time (i.e. in between holes). Although this is true, many tournaments tend to adopt the 'one ball rule', which means you can only use one type of ball. By the way, nearly every tournament I play in follows the 'one ball rule'.