This was "fixed" two years ago:
Can we switch the "Visited" and "Unvisited" link colour on beta Stackexchange sites?
It seems like the "fix" was by design - they made the visited links darker than the unvisited links. I think it's arguable that that may have been better in the previous checked beta theme, but in the new theme, I tend to agree with you. If I loaded that page I would assume that the 2nd link is the only one I haven't been to. The "lighter" color behaves in this case more as a fader than a brightener; I'm pretty sure the intention of highlighting "new" links is to make them stand out as "brighter" not fade into the background. The latter seems to be the effect achieved here.
Here on meta, for example, visited links are lighter, though admittedly the difference is much more subtle than on SO and dba.SE, where the opposite is true:
I might suggest changing your title to:
Can we switch the "Visited" and "Unvisited" link colour on beta Stackexchange sites back again?
(I also think this came up more recently, but couldn't find an adequate duplicate.)