The term palette swap originally meant shifting the colors of a created art asset in a game. Make them red instead of blue and you get a brand new character/item/weapon/level without having to put the hours into creating it, or the memory to store it.
An ingenious use of palette swapping came from the first Metroid. This was a very ambitious game for the technology at the time, and in order to save space, they created a new weapon (ice beam) by simply changing the color of her gun to blue.
The ice beam temporarily freezes enemies and allows the player to use them as platforms. This is an integral part of Metroid’s design, locking away parts of the game until a new ability grants access. This was so effective, the term Metroid-vania was eventually coined to describe side-scrollers that used this mechanic.
Super Mario Bros. used this technique heavily. Changing Mario’s clothes to white denoted the fireflower power-up, while making him flash during invincibility. Red Koopas turned back from ledges but their green counterparts foolishly walked off, even to their own demise. And of course Luigi was created by swapping the main color of Mario to green, giving the second player an identity.
Who can forget the eternal rivalry of Ryu and Ken? They even had identical move-sets when first introduced in the original Street Fighter, but this was a Mario/Luigi situation as players could only control the two main protagonists to face each other, with the winner going to challenge the computer controlled opponents. Street Fighter II: Championship Edition gave Ken a different Shoryuken arc and Ryu’s Hurricane Kick a knockdown.
Akuma and Dan were introduced later as evil and goofy variations respectively. Minor tweaks to hair, eyebrows, and clothing can go a long way to differentiate the same core model.
Sub-Zero and Scorpion were much more literal palette swaps. The same actor and costume was photographed in different poses to provide the difference. Changing their special abilities however, makes all the difference when it comes to fighting games. They may look nearly identical, but MK fans would never call these two the same.
The Mortal Kombat franchise was criticized for relying too heavily on swapping with the introduction of Ermac, Noob Saibot, Reptile, Smoke, and Rain all using the same model. I’d argue that if the special moves are unique, it’s better to have a new swapped character, than none at all. When creating a game, resources are finite. Reptile was my go-to in MKII and nine-year-old-me didn’t think he was a boring re-use of assets, he thought he was a cool green ninja that could turn invisible.
Game development is one of the most grueling art forms around. The combination of art with technology presents many challenges that are overcome with skill, ingenuity, and sacrifice. The palette swaps I mentioned were all born of memory limitations. Developers used swapping intelligently to create wonderful gaming moments that are still remembered today. While modern gaming rarely deals with storage issues, there will always be technological limits when trying to push the creative edge. Creating better-looking assets, filling the screen with objects, and maintaining a steady frame rate with limited load times will always be a challenge. Swapping palettes and other tricks are a part of the process, and I’m sure we’ll see more as time goes on.