Super Bowl!

[monster]

Ok. sorta cleared up...it varies and even within sports and leagues...

from Wikisourceofallknowledge:

For home and away jerseys, teams often use white (or another light color such as yellow) as the main color for one jersey and the team's primary color as the main color for the other jersey. "White home" is the convention in baseball (MLB), basketball (NBA, NCAA basketball) and college hockey, while "white away" is the convention in football (NFL, NCAA football) and NHL. However, the conventions are not rules, and often the home team has the right to choose which jersey it will wear, with the visiting team forced to choose a contrasting color. For this reason, teams often create a third jersey, usually with a secondary team color, to ensure that they will always have an appropriate selection for the game. The term "third" or "alternate" typically refers to this specially designed jersey. Throwback jerseys can be considered additional alternate jerseys, but they are generally only used for special team games and not for the "third" purpose.