I mean, when I hear the word "compositing" I definitely imagine something that involves "alpha" blending, and doing that nicely (instead of a literal alpha calculation) is going to involve colour management.

That's on the Wayland team though. They drew up the new API boundaries and decided that all window managers would now be in the business of compositing.

If I wanted to put it most uncharitably, I'd say they decided to push all of the hard parts out of Wayland itself and force everyone else to deal with them.