You can only downgrade to whatever operating system your machine had when you first took it out of the box. For the rMBP, that means Lion, Mountain Lion or Mavericks, depending on when you purchased it.
You can only downgrade to whatever operating system your machine had when you first took it out of the box. For the rMBP, that means Lion, Mountain Lion or Mavericks, depending on when you purchased it.
I am almost sure that it's a bug. It does not happen on my 2007 iMac at all and that's because it's too slow to go to the grey screen before it should. On the other hand, on the rMBP it happens all the time. The other day, the screen did not only turn transparent (like in the picture) but I could still see a little bit of the top of the dock so I think that is enough proof that this is not a feature but a bug. I wasn't quick enough to reach for my phone to take a picture.
I am also experiencing this issue as well. Glad to see there are others out there that are enjoying this bug. I however would like it fixed as I find it rather annoying. Hopefully there is a fix in the works at some point.
The only way I got this fixed is by a clean installation. Other things I tried, such as resetting SMC, PRAM, repair permission etc, does not help.
Another thing is that I got this very symptom when I upgraded to Yosemite today. This time, a clean install did not fix it. I have no idea why this happened and whether there is a simple to fix it.