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.
This is an intended feature. You have enabled the "super secret settings", which are rendered with post-processing. To reset the setting, just restart your client.