Created attachment 119855 [details]
Example animation

SUMMARY
Because Rec 2020 linear color space is both linear and allow for values higher than 1.0 (which are not clipped to 1.0, but shown properly), onion skin isn't that helpful on HDR or linear animations. It looks dark and doesn't really pop up as it does on my non-HDR laptop (which has a much lower grade display).

It looks like the reason for that is the color selector that doesn't allow for anything else than 8bit integer or values bigger than 1.0.

SDR animation isn't in a better situation though, because all SDR content is clipped to 80 nits, which is very low. But because there is nothing more bright than that on the canvas, it still somewhat work.


STEPS TO REPRODUCE
1. Make an animation using white circles. (Use HDR setup.)
2. Turn on onion skin.
3. Make sure the colors used for onion skin are the brightest possible red and the brightest green.

OBSERVED RESULT
Onion skin is rather dark, the contrast is not enough.


EXPECTED RESULT
Onion skin in 100% opacity and 100% of tint should be bright and pop out out of the image.


SOFTWARE/OS VERSIONS
Krita version: 4.2.0-pre-alpha (git fb08951)
Windows: 10
Qt Version: 5.12.2