https://github.com/Vazkii/Quark/blob/d51cad7bdb777a71a438a9d7cc27e75068b4694e/src/main/java/vazkii/quark/client/feature/GreenerGrass.java#L120

Tough as Nails no longer has season colours so the incompatibility should probably be switched to Serene Seasons here.

Note that Serene Seasons colours do still affect the world even with Greener Grass enabled, however it greatly reduces the effect making it almost impossible to see. Here is a screenshot of Serene Seasons with and without Greener Grass.