A trap most people fall for. In this case, people normally confuse the game rival with the anime rival. And most people call him "Blue" instead of "Green", although that last one is dependent of where you live.
Actually if you're playing FireRed, the Opposition being LeafGreen (Starting a Nuzlocke challenge of that soon)then it should be green :L I'm gonna call him whatever though ^^" I don't mind he name as long as it's cool. I'm doing a five gen one, an since I don't believe you name your rivals in gen 5 the others may simply be Locke :I