Thank you both for the suggestions re. changing the colour tone of Windows 10 to reduce the amount of blue and lower the colour temperature. I am already doing something similar.
* I have [url=https://www.groovypost.com/howto/calibrate-monitor-color-display-windows-10/]calibrated the monitor colours[/url] to have overall less blue, similar to Windows Night Light - carefully done to preserve relative colour accuracy, so photos and movies etc still look good. This is similar to having f.lux or the Win10 Night Light enabled all the time. I don't change it at different times of day. Technologically this is also a good solution because colour calibration is done through the graphics card, so it automatically applies to everything (full screen movies, games, etc). Specifically, Windows uploads the colour calibration profile to the graphics card when Windows starts, and then the graphics card does the rest.
* Windows 10 apps are [url=https://www.howtogeek.com/222614/how-to-enable-windows-10s-hidden-dark-theme/]set to use Dark Mode where possible[/url] - since the March 2019 update this includes folder windows (Windows Explorer) and most - but not all - Windows 10 components
* I have set the Windows 10 accent colours to something dark
* Windows 10 [url=https://www.softpedia.com/get/System/OS-Enhancements/Classic-Color-Panel.shtml]system colours are set[/url] to a generally dark palette chosen by me, for example window borders and title bars are dark. For reasons already explained, I do not choose a full "white text on black background" colour here because that breaks a few applications (hard-coded black text would become invisible with a black system background). Obviously I do not want to be changing my Windows system colours for each different application I use, anyhow Windows requires a re-logon to update the colour palette so that would be practically impossible. The best compromise is black text on a mid-range background. The mid-range Windows system background colour is giving rise to the severity of the Pmail colour issue raised in this suggestion.
* I have disabled Cortana in the Windows 10 task bar (an ugly white search box)
* A nice Chrome extension, Stylish, allows the colour scheme of any website to be over-ridden by a user style. Stylish is a popular tool and therefore the community has created good 'dark' user style for many popular websites, which you can choose and activate for each site, so I have these for Google, StackOverflow, Github and others that I use regularly, all of which have the tyrannical black text on a white background.
I should probably write a blog post about all this, if I had a blog...