Just realized last night that I was playing without HDR turned on. The HDR option was grayed out in Assassin's Creed Origins. 

I have a Vizio TV and had to switch HDR on in the input settings. 

I followed the Xbox procedure but turns out you still need to check TV settings. Xbox will allow to check off Allow 4K and allow HDR even if the option is off on the TV.
 

Turning on HDR

To check, press the Xbox button   to open the guide, go to System > Settings, choose Display & sound > Video output, and then choose Advanced video settings. Both the Allow 4K and the Allow HDR settings should be checked if you want HDR on.

Also, check your TV's settings menus to make sure HDR is turned on. Your TV must also support the HDR10 media profile to display HDR.

Don't make the same mistake check your TV setting. 

https://support.xbox.com/en-US/xbox-one/console/checking-your-tv-4k-hdr-capabilities-on-xbox-one

STATE OF DECAY 2 HYPE WOOT WOOT.

A lot of people have learned this lesson the hard way with HDR TVs. Myself included. HDR ain't on unless you turn it on.

Makes you wonder though.... if you don't even realize its not on, how much of a difference is it really making?

It was 4k on Xbox one X... but ya the difference isn't major. 

You actually had me doubting myself for a second. Then I remembered I downloaded that "Insects" tech demo and it tested for HDR.