[Soli]

I am using latest stable kodi on Fedora Linux and having an issue with all 4k releases. At this point I have about 40 movies that are x265 encoding, mkv container, 10-bit, 4k and they all look washed out / under saturated. The monitor I am using is not HDR so I don't expect 10 bit colours but I would expect it to downscale one way or another and look like more common 8 bit video. I am also assuming that it is 10 bit colour that is causing this but perhaps it's x265 encoding. It also looks the same in VLC player but it also stutters so it's clear that support is not properly implemented there yet. Default windows 10 player looks more like 8 bit video, but I feel there is too much loss of definition. MPV player handled it the best and colours looked like 8 bit on an 8 bit monitor.

Why does 10 bit video look under under saturated in Kodi and other players? Is there a way to fix this issue? I feel like I might be missing something simple but I can't find any references to an issue like this.

There is no player/OS/other software or hardware that handle this right - doesn't matter if its AMLogic or other socs, Android, OSMC, OPENELEC, LIBREELEC, Shield, MPV, VLC, Windows, WMP, Linux. You are probably lucky that MPV has a somewhat approximation  that looks okayish. 

To convert from HDR/BT.2020 to SDR/BT.709 one needs the following information of the BT.709 display: Gamut (already given..obviously), black level, white level, gamma. There is no single fix that works for everybody.

Luckily for you I've made a few 3DLuts with a black value of a typical lcd monitor: https://mega.nz/#!5uQAEC5Y!_sfHlVBKsNs1t...j7zqEFFCKE  Use the one that looks the best for your display. 

Since Kodi already supports 3DLuts it would be easy to implement proper support for hdr/bt.2020->sdr/bt.709 conversion, but it seems the devs don't want this feature  
It could be done via a set of presets (each LUT is about 100MB and one would need maybe 3 presets for different black levels, 5 for different whitelevels which means 15 in total. Ideally one should also have these presets for gamma 2.2, 2.3 and 2.4, so that would mean 45 luts in total which would total about 4500MB but would compress at 1:7 the size....or even better: rip the code from displaycal and make the luts on-the.fly. Anyways, digressing...