Sometime in the PS3 era, graphics got so realistic that…

Let’s back up a second. Go play Ocarina of Time. OoT has wall climbing mechanics, but Link can’t just climb any wall, it has to be a climbable wall, and that is denoted by a different texture. Most commonly vines, but there’s a ladder-like texture on a wall on Death Mountain and rough brick in the Spirit Temple. And one wall in a Skulltula nook that isn’t textured, but Link can climb it anyway.

The 3D environments on the N64 were pretty rudimentary; big chunky rectangles. A couple generations of console later, you get pretty realistically noisy environments. And you’ll have the exterior of a building or a pile of debris or some other set piece that has a single intended climbable path. Where older games would just…lay out a weirdly rectangular patch of climbing vines, now your character is supposed to climb pipes, ledges, window sills etc.

Not everywhere in the world is climbable, so they started tinting actually climbable surfaces a distinctive color, often yellow, sometimes white. The new Tomb Raider games do this, later Final Fantasy games do this, Horizon Zero Dawn/Forbidden West do it, etc.

The biggest extreme is Mirror’s Edge. The game’s primary mechanic is parkour, so the “paint climbable edges yellow” technique is elevated to the game’s whole aesthetic; the environment is stark white with parkourable elements tinted bright red. Looks cool and stylized while also allowing the player to process the visual information fast enough for a parkour game.