Is there interest in adding support statistics for System Colors?
It is described as deprecated, but there is no clear substitution to it (appearance property is still being discussed).
CSS4 draft points that it can be seen as 'a security risk by allowing a webpage to "spoof" a native OS dialog' and prompts authors to not use it and browser to map these keywords to default values which don't use user current system settings.
Even in MDN, there is no browser support information, just that 'it is not supported on all systems'.

It would be interesting to have this information about which browsers still have this functionality fully working and which are doing what the CSS 4 draft prompts them to.
I encountered what appears to be a valid use case for it: adding system native outline color to rich custom form controls (like custom radio selections, etc), e.g . Or maybe this is just me being ignorant of a better way to achieve it.