That link was great. I stumbled across it yesterday when trying to fix HDR on my AVR X4200. The step which worked for me was:
"Disable the video conversion in the AVR."
Something as simple as that (default) setting was killing HDR, resulting in washed-out colors.
Now to see if my new RPi 4 with LE can reliably play 4K content for entire movies (my S912 with CoreElec struggled).
Cheers, Carl
I believe you may still be getting sub-par colours in the current Pi 4 HDR builds - as I don't believe Rec 2020 gamut (which is the gamut HDR10 and the 'in the wild' HLG uses) is being flagged, so whilst the colours look less washed-out than when the HDR EOTF was being blocked (and your PQ ST.2084 content was being displayed in SDR), the Pi 4 still outputs Rec 2020 as Rec 709.
Some TVs may switch to Rec 2020 when they detect an HDR EOTF I guess (though that's a bit of an 'out of spec' guess), but certainly my Sony TV will display Rec 709 gamut stuff in Rec 709 with an HDR EOTF (which means the colours will be less vibrant than if correctly flagged as Rec 2020 - which I can manually force and which brings things closer to what they should look like) (*)
(*) The YCbCr->RGB matrixes used for Rec 709 and Rec 2020 are slightly different - but the differences between them will be harder to tell. (The difference between Rec 601 SD and Rec 709 HD are more marked ISTR)