I remember the D2 perspective mode was a neat trick but it made the game kinda fuzzy and broke core graphics features such as my character wouldn’t be green when poisoned.
The green was a palette trick. The Direct3D mode used high-color mode, so that trick wasn’t free. It did draw a green light halo around the character’s feet instead, though.
You can key on any color; green is the most common mostly because it's pretty far away from the range of human skin/hair.
You also only need to worry about this when you're doing effects shots. If you're doing relatively naturalistic filmmaking where your set/location isn't gonna be replaced, there's no need for any of that.
