He's complained about it since the time Nintendo Select titles on the GameCube had the yellow border and side added to the covers to distinguish them as such. I'm sure you could do a search of his posts and come up with a bunch of them complaining about this many times.
But the truth is, I give him a pass on this. I've never liked the three GC cases I've got with the yellow GameCube logo. They just stick out from all the other titles that have the black side. I also try and find the original box art for the Wii games as well. Truthfully, I've never liked how a few N64 game cartridges were colored differently either. They just seem like they don't belong. Plus, buying the original box art makes it seem like you were an early adopter and played the higher price for the game instead of showing that you are a cheap, tight-fisted, penny-pinching, miserly, third-rate, bargain bin game buyer in front of any people who see your game collection.