Originally Posted by HDdoggy
Those play correctly in HDR on my native TV Youtube app but not my Firestick 4k. I've tried so many settings and resets and swapping HDMI ports but my TV plays them all in this washed out color that I think is related to choosing the wrong color space after detecting they're HDR. Prime Video plays in HDR correctly so it's something related to just the Youtube app and my TV as far as I can figure.
To get HDR you need to ensure the H9F's HDMI port is set to enhanced, I suspect this setting is per port so after setting it on the port your Firestick is connected to make sure it's saved by selecting Apply Picture Settings to current source. At first I would confirm you can play anything on the Firestick in HDR using another app. If that's successful I'd look for an HDR enablement setting in the YouTube app. If no setting exists it's possible the app doesn't support HDR.
Another slight possibility concerns the transition between HDR and SDR I've encounter using an HDR enabled PC with SDR games. While the TV will detect the transition of HDR to SDR, the color palette is usually off resulting in an oversaturated appearance with the HDR to SDR transition and a faded appearance with SDR back to HDR with the TV still detecting an SDR source.
This is probably more of a Windows 10 HDR issue and/or the games that weren't designed to deal with it than the H9F however it still required a Picture mode change to properly pick up the HDR mode and enable the correct palette after Windows 10 HDR mode was cycled. On the Windows side when starting an SDR game I could just turn off HDR before running the game, however I find it easier to just Window Key back to the desktop and then re-enter the game and walla, proper SDR palette.
So while playing HDR YouTube content on the Firestick try changing picture mode giving the H9F a chance to rescan and see if it doesn't pick up HDR.
Another tidbit I'll mention concerning the choice between native or auto color palette which doesn't affect recognition but just appearance. Native looks slightly richer so I've gone with that at least with my PC source, your mileage may vary.