Ok, it has me confused a little but if the 5.11 test version has it I can give that one a try.
To complete the reason why I thought it already was implemented was because I saw the dark mode used on the JMRI.org webpage already, for example these 2 places:
The images in these 2 links are in the dark mode.
The mentioning of the dark-mode was in the release notes of the 5.9.7, I assumed it was part of all releases after that but it seems I was wrong.
I'll go give the 5.11 a try soon.
