Fire Mario wears a feather in Super Mario Land 2
Super Mario Land 2: 6 Golden Coins is one of the more underrated Mario games. It's the second Mario platformer on the Game Boy, and it is also the first appearance for Wario, the bad guy that stole Mario's castle.
Fire Mario looks a little different in Super Mario Land 2: 6 Golden Coins because of the Game Boy's limitations
At least the plot is a bit more refreshing as it isn't about rescuing a princess, which has been really overdone. I'm not saying you can't have a plot about rescuing Princess Peach, but just don't do it almost every single game.
For the kids these days, it would be crazy to imagine playing a Game Boy (which originally came out in 1989), a portable video game system that is monochronic and runs on 4 AA batteries. But those were the days. Because of the system's limitations, it results in developers having to do things a little differently.
In every other Mario game, when collecting a Fire Flower, Mario will transform into a different look, usually he will be wearing a white shirt, white cap and red overalls.
Because the Game Boy doesn't have a colour display, there's no real way of representing Fire Mario in different colours. Instead, they added a feather on top of his head to distinguish him from regular Super Mario. The feather looks exactly the same as the Cape Feather in Super Mario World.
Hmmm, Mario throwing fireballs with a feather on his head, this sounds quite similar to the outrage caused by a feather-wearing Mr. Game and Watch in Super Smash Bros. Ultimate. Such a reference to a native headdress is considered "cultural appropriation" which is racist and offensive to native and indigenous communities in North America.
Super Mario Land 2: 6 Golden Coins has never been remade, but if it does it should be in full colour and I'd imagine Nintendo would probably correct this depiction of Fire Mario to his normal red/white look.