God damn it, I submitted it before writing out the issue.

As for the issue, I have tried applying the Greener Grass effect to the "Giant Tall Grass" block from Environmental, but it did not work even after restarting the game. Environmental is still not officially released so I tried adding blocks from other mods and it did not work with them either.

The other mod I tried applying the effect to was Farmer's Delight.

MC Version: 1.16.4
Forge Version: 35.1.28
Quark Version: q283
Farmer's Delight Version: FarmersDelight-1.16.3-0.2.4b

Here's my quark-common.toml (changed to .txt so I can upload here)
quark-common.txt

I managed to add it to several modded blocks, but it didn't work on all of the ones I tried- sometimes it would work for some but not all of the blocks added by the same mod. My guess was that those blocks don't use Minecraft's grass coloring scheme.