The newest Grim Dawn update has done some interesting things. I no longer need to use the Grim Internals mod as a lot of the features I used it for are now baked into the game.
However, I still need my Rainbow Filter.
IMAGE
Image Credit: SudoMistress

How to Install Rainbow Filter when on Linux
- Go to Rainbow Filter
- Download the file of your choice. For me it was [Files] Full Rainbow (English)
- Extract contents to directory of choice. The directory will be called
Grim Dawn
. Inside it will be another directory calledSettings
and in that directory will be all kinds of things. - Open Steam
- Right click on Grim Dawn -> Properties -> Installed Files -> Browse…
- Move the
Settings
folder to the folder where the game is installed. - Profit