Crash occurs when the colorizing brush would show up in JEI. Hiding the brush in JEI seems to temporarily fix it.

Assorted Decor 2.0.9
MC 1.16.5
Forge 3.6.1.4

crash log
https://gist.github.com/judicius/4b57909ff24901461792a1b29626064b

Hello, I got the same crash. It also crashes when middle-clicking a colorizer block. This happens if Twilight Forest is installed.
https://gist.githubusercontent.com/natanfudge/b60a447424e46c7dda12ede0fcf56851/raw/6ede6e5d6b4910fbafe00e1147472b651310de3d/crash.txt

My environment apparently is broken. I think I have a fix that will work but I am unable to build right now...

Will take a look once I have some more time

Thanks!

Alright it should be fixed with 6970025.
It is published in assorteddecor-1.16.5-2.0.10