My TV is set to Full, I'm connected to a Marantz NR1606 4K receiver, and Dynamic Range is grayed out. If I change the resolution to 1080p it is no longer grayed out and my blacks are no longer washed out. Is this a bad HDMI cable or something else? Thanks!
Edit: This is for the Shield TV recently updated to Marshmallow.
I did a bit of testing with this on my Samsung UN55HU7000FXZC Scratched my head for a bit, until I read the manual twice. My TV only supports HDCP 2.2 on the HDMI/MHL (HDMI-3) input. So that's where I have my AVR/Shield connected. Unfortunately the modes supported on this port are quite limited. The other HDMI inputs support a plethora of rates, but they are not HDCP compatible (so no Netflix 4K without HDCP.)
I am able to set Dynamic Range to full on 1080p 60Hz and 4K 23.976Hz - and it looks great. No washed out grey-ish black anymore. Unfortunately the UI is very sluggish at that rate.
Check your manual - you may have the same limitation as my TV. For reference, manual for mine is at http://downloadcenter.samsung.com/content/UM/201506/20150604125403347/ENG-US_NUATSCH-1.119-0527.pdf
On page 201 it shows the table of supported modes for each HDMI input. At 50/60Hz, mine only supports YCbCr 4:2:0. At 24/25/30 it supports RGB, YCbCr 4:4:4 and 4:2:2.
I guess I will try it on the other inputs and see if it works (it should..) but then I give up any 4K source that requires HDCP. Such Fun!
The release notes explicitly state that full range is only enabled for rgb outputs.
If you have a 4k TV, it is mostly running in y cb cr.
So as of right now, this is expected. I would hold off on it though. Enabling full range on TVs that don't support it can lead to over saturation