This consistently happens at File Vault password prompt time, right after booting. It started appearing after the latest update to 10.11.4.
The machine works fine though, so I wonder if this is just a clear-screen glitch or something more serious ...
MacBook Air (13-inch Mid 2013), OS X El Capitan (10.11.4)
Reset PRAM. http://support.apple.com/kb/PH18761
Reset SMC. https://support.apple.com/en-us/HT201295
Choose the method for: “On Mac notebooks with non-removable battery”.
If this does not help, please contact Apple.
Genius Bar reservation:
For the records: didn't help, boot screen still looks the same.
Thanks for these reset hints though, they might be useful at another time.
So the trick is to change the background color of your desktop. Then log out, then reboot. That color sticks, really, for good.
Changed the desktop color to something different, but it's still the same.
However the corrupted image is now gone and that's a good thing 🙂
Corrupted screen at boot time file vault password entry?
