Which computers will receive the black boot screen with the white Apple when upgrading to Yosemite versus the white screen with the dark Apple?
I think all retina screens receive black screens white logo and all non retina's are the opposite. At least my retina's are black and my non are gray, so far.
Well I have seen some MacBook Airs have it so I wonder if it has to do with EFI.
Possibly. I know in the PB's of Yosemite my boot screen was black, but shortly after Yosemite was pushed to the masses and I updated to 10.10.1 it was back to gray. (On my '09 MBP, that is...it's sorta my test laptop)
It changed over to black on my rMBP sometime during the early public betas. At first I thought it was something to do with retina or non-retina (because the boot screen was light on the 2010 iMac), but later I clearly spotted a black boot screen in one of the 2014 Mac mini reviews and the display was definitely not retina.
It might simply have to do with the age/type of the hardware. A mid 2012 rMBP is probably the oldest hardware to get the black screen without some sort of firmware hack.
I wonder if there is a way of editing yosemite so we can choose black or grey ?