Greyscale stops working upon opening built-in launcher

I installed Nova launcher, for obvious reasons.
Now, everything works fine after a reboot, and up until the point that I go into the built-in notes app to start using the included pen. Launching that notes app runs something, somewhere, that screws up grayscale in Nova. This makes every single app icon look like a black box. Strangely, the tiny icons in folders are shown as dithered (fake greyscale) instead.

I tried switching every refresh mode known to man, but only from the notification area button. If there is a setting buried deep somewhere I probably missed it.

Also note that this does not just affect Nova, it also affects the profile pics in the RiotX app. So it is more systemic than just a weird launcher app.