I have exactly the same problem with Windows server 2012 R2 VDA
It is grey screen on latest release of the client but on older client it was a black screen.
Server 2012 R2 HyperV hosts
Server 2012 R2 across the board for controllers and storefront
(Basically all 7.6. ISO install with Hotfix 1 for Broker, Host, MCS, MonitorPSS, Monitor SRVC and ConfigMgrWOL)
Server 2012 R2 VDA tried with 7.6 through 7.7 and 7.8 later releases to see if there were improvements to this issue. All created with MCS not PVS.
Enabled legacy graphics and disabled DCR in citrix policy
changed the registry settings as above for graphics mem etc
I even disabled themes!
Grey screen on logon. checked and the user profile creates ok
logged on via RDP fine and set to basic windows theme...disabled themes service
Restarts a plenty and same results
Even tried disabling the hyperV graphics adaptor in line with the issues seen with VMware and the SVGA adaptor. same result.
We had a similar issue on 7.6 last July with Server 2008 R2 and the hotfix download ICAWS760WX64026 resolved this issue.
Now we are seeing the same now deploying server 2012 R2 desktops.
Interestingly the VDA needs a restart after every logon attempt via ICA as it appears to lock up and won't allow user logon. There are no events in the event logs to suggest an issue with licensing, graphics or otherwise.
I did have event 1004 composite redirection is not available because client protocol version 0.0 is not supported until I disabled DCR. none since.
Our 2012 R2 Xenapp servers are fine on the same platform.
I have destroyed the delivery group and catalog and rebuilt many many times over with the same results. if we didn't have Tintri cloning for our master Windows image I would have lost my mind by now! I have also tried another master image from scratch without cloning with the same results from our SCVMM library.
I cannot take the platform down to upgrade to 7.8 without having to update hundreds of desktops and I'm not convinced that will fix the issue. Unless of course someone is successfully running 2012 R2 VDA's on 7.8 controllers with SF 3.5?
If anyone is running 7.6 2012 R2 VDA's successfully with hotfixes delivered by MCS, which combination of hotfixes gets this thing to work?