I have a KU6300 4K TV and I cannot get 4K/60Hz/4:4:4 with my RX480 (Only 4K/60Hz/4:2:2). I am connecting HDMI->HDMI1 in with HDMI UHD Color on. After a lot of trial and tribulation I find this thread: Catalyst Drivers force 4:2:2 chroma confirming that the issue is indeed the RX480/crimson drivers. I attempted the solution li7in6 gave at the bottom of the thread, and I cannot get that method working.
(saying it's a permanent fix) using the Custom Resolution Utility and now my TV is stuck on 4096x2160 (It's only a 3840x2160 TV and changing the resolution in Windows 10 won't do anything), I cannot get higher than 4:2:0 now (before I could get 60Hz/4:2:2) and color look terrible. I can't seem to reverse any of this.
I don't know what to do at this point. Suggestions?