Well, I'm making a GregTech-based skyblock pack and want End Stone to use something a bit more later in the game than Lava. I wanted it to use Nitration Mixture, but when I set the fluid name to "liquid.nitration_mixture" the recipe doesn't exist.

Nope, that's simply how GregTech generates its fluid names. I was thinking that perhaps it doesn't work because it starts with "liquid.".

In 1.12.2 mod names aren't used in fluid ids.

This is GregTech Community Edition: https://github.com/GregTechCE/GregTech

Side-issue: its fluids show up white in Ex Nihilo Barrels. Might be related

Ye could possibly be connected, but I have no idea what might be the cause of either, if I find time this weekend I'll check it out more deeply

Huh, ok then. I'm away for a week so I can't really retest everything.

Apprently gregtech is doing wierd stuff with their fluids, as in not even Forge regonizes them as a fluid and adds a bucket variant of them.

Those are all buckets, none of which are Gregtech.
In this case I can't really test it either as I have no idea how to obtain the fluids on a different way for quick testing purposes.
I suspect that those two issues have something to do with each other, but not sure.

And regarding your colorless issue, can't really replicate, atleast helium has a color in the barrel for me

Welp, tested the recipes and that seems to work just fine as well:

https://gyazo.com/abda45cc791bf3f59cc4137836e04be2

Closing this for now, if the problem is still there when test it again, just open it again or make a new issue and describe your steps closely so I can reproduce it