Blank Gray Screens When Dual Displays are Attached, Color Profiling on Dual Display

With dual displays, reboot the Mac and one is presented with nothing but a gray desktop—no login dialog, nothing. Rick S writes:

I updated to 10.10.4 and now my multi-display set-up only allows me to see the login screen when I have just one display plugged in.

When I startup with both displays plugged in I just see a blank grey screen on both displays. Once the log in screen appears on one screen (can’t have two displays plugged in) I can plug in the other and all seems to work as before.

Both thunderbolt cables plugged into different buses. I have a PA322UHD and a PA301W. Any thoughts? Seems like a strange bug. Any thoughts. 10.10.3 was working well for me.

Also, on a separate monitor related note I can’t seem to get the color temperature of my two monitors to match. Calibrating both monitors with spectraviewII. Any thoughts?

This Apple Core Rot bug has actually been around since 10.10.3, maybe even 10.10.2 (I forget). It happens to me 100% of the time when rebooting. It’s rather obvious that Apple no longer bothers to test dual displays much, if at all—Photoshop can’t zoom properly, color profiles don’t work properly on dual displays, and many more issues abound.

Workaround: turn off the 2nd display using its power button for a moment; the login dialog now appears. Turn the 2nd display back on, login and all is well. It is not necessary to unplug the display.

As for color matching on two displays, I cannot get that to work either—yet both are truly calibrated* with NEC SpectraView II. As far as I can tell, Apple has also broken color profiles on the 2nd display and only the primary (main display) is correct.

* See Understanding Display Calibration: Real vs Faux Calibration.