Certain linedefs are appearing darker than others

[Chloroxite]

Title.

I have no clue what is causing this and I would like to fix this as soon as possible. Any advice is greatly appreciated.

[boris]

It's called fake contrast. In GZDoom you can control the behavior through MAPINFO.

 

https://zdoom.org/wiki/Fake_contrast

 

[Chloroxite]

Thanks, I think that might actually be it.