Adding a second kind of shiny Pokémon

Okay, so I was wondering if anyone knows where, exactly, all of the shiny scripts are located. I found the stuff in the basic attribute accessors, the shiny flag and whatnot, but I can't find the stuff that actually looks for the right sprite to call.

What changes are you making, might you ask? Well, and feel free to rip off this idea if you like, I'm creating an area where all the Pokemon have a different coloration completely unique to that area, sort of another shiny flag that gives them a third coloration total. No longer will 17% of them be green in color. Due to how it's encountered, it's called Nightmare or DarkWorld coloration, but not all of it is going to be dark.

Wouldn't it make more sense and be easier to define this in multiple forms?

I need to describe it almost exactly like shiny.
Forms WOULD make sense, but I don't think that's the answer here. If it was one Pokemon, that would be okay, but it's ALL of them. It behaves almost as if shiny were area-specific, if you think about it.

If there's something I'm missing, or I'm not understanding correctly, feel free to elaborate.

Search by "tshiny" and "Graphics/Battlers" at PokemonUtilities script.

Okay thanks. I actually found PokemonUtilities and some of the scripts, but I think that should get the rest of them. I'd bookmarked it to do "When I got done with everything else". XD