Shal,
It's possible I misread your answer below,
But I use Chrome almost exclusively on an XP system, 2 Windows 10 systems and my Samsung Galaxy S4 android phone and the blue links consistently change to black after the message is read.
Highlighting for visited links is a browser feature, but Groups.io is using a style sheet to select the colors displayed for visited versus not visited links. The distinction is whether the message page is already in your browser's history or not.
E.g. I'm on Windows and Android, and there is no distinction between
messages that are new or old (read).
I hadn't noticed that, but for Chrome on Android you're right. But for Firefox on Win10 I'm seeing link coloring.--
Bob Bellizzi
The Corneal Dystrophy Foundation