Rainbow wavy strobing in Minecraft

What I expected to happen-
Load a new creative world fine with no visual changes

What actually happened-
Disco strobe lights immediately filled my screen. At first I thought this was a prank by Mojang, but then found that it was due to the new graphic settings added.

How to replicate-
I loaded a creative world to test things and 'Enable Post-Processing' set to ON. When I turned that off, the disco screen stopped.