[Mount81]

Whatever you may have referred as "dither" or "dithering" have confused me much anyways. Dithering. -> So -technically- my suspicion would have been right, if you've meant and used the word fitting to it's meaning. So yes, all sort of "dithering" -in this case- would mean of something non "native" and altered picture for the sake of "better than worst" quality (which "worst" in this case would be 10bit simply regulated to 8bit) and the native "non dithered" solution is simply the unconverted 10bit output. Even the 10bit to 12bit up-conversion is far better -and rather seamless- than the 10 to 8bit down-conversion.  I couldn't think of anything else, that you meant the dithering rather to the colorspace conversion... Or what exactly?

Still, if you aren't -somehow- forced to react that head bitingly conflicting to any opinion towards your understandings, than would you be just that kind to rather choose a nicer way for your clarifications?  Sorry that I didn't know that RGB is limited to max 8bit on PC in the case of 444 (>30Hz), my trigger point was that 10bit it is always possible on all kind of Hz (from 0 to 60) with some YCbCr colorspace setting. For example on 23.976Hz (and for anything less than 50Hz) you can even have 444 / 10 bit on 4K, which is the very best option in the case of dedicated media players (the one-step RGB conversion is just left for the TV in this case).

Tho' it's effect in general still isn't denied by me, but I would be still highly surprised if you could prove somehow that colorspace settings have bigger effect on the overall picture and color transition quality than the 10bit vs 8bit difference has.  I.e. let's take a native 420 10bit video, made to converted on output (on whatever Hz) to 444 8bit and 420 10bit by the PC player. In which case do you think you will you have better overall picture quality?