Every research-driven publication I've read has always said that different colors for visited and unvisited links are markedly better, and having them are the main reason I child themed twentysixteen at cjshayward.com because Jakob Nielsen's original, and revised, top 10 mistakes in web design states that colors should look different. So does Steve Krug in a later edition of Don't Make Me Think!. How to mark visited vs non visited links says, "color coding of some kind is still advised to distinguished visited links.".
The last item I quoted links to a no-longer-existing cite, and was written in 2013. Which brings me to a question:
Every research finding I've read underscores the preferablity of visited and unvisited links looking different...
...but there are precious few sites make visited and unvisited links look different, even if one of the exceptions is Google...
...Which raises a question if the near-universal domination of single-colored links is so vast and so complete that separate colors are unfamiliar and will register with a user as a UX feature useful in knowing where you've been and where you haven't.
Have there been any recent studies about whether users are familiar enough with the cue of different colors between visited and unvisited links for the basic cue to register?
The trend is not complete; a comment on Visited links: expectations and accessibility lists Google, Reddit, and Craigslist as still having two colors. However, the twentysixteen theme does not even allow separate colors, even in an option that is off by default, and my defect was rejected on the assertion that it would break existing sites (a point I would contest for an adequately good implementation), even though Wordpress's own guidelines say "Two separate colors, please."
So will users still benefit from a UX feature that has come standard and for free since Netscape 1, or will the oddity of some links being a different color simply not register?