Sodium 0.2.0 breaks colormatic. It has not been released yet (this is the commit that broke it I believe: CaffeineMC/sodium@f4d0820), but there are plans by CaffeineMC to release Sodium 0.2.0 (for 1.16.5) soon.

There are currently no plans for continued development of Colormatic for 1.16.x. Current efforts are focused on a 1.17 release, after which all updates will be to the 1.17 version.

That being said, the issue should be fixed in the 1.17 version, and it may be possible to backport a fix.