I can't seem to determine which questions I've browsed to on superuser based upon the coloring of the link. As far as I can tell (maybe I'm color blind), there is no difference between the coloring of browsed and un-browsed links. In contrast, on SO/SF/META, the coloring of browsed links is pretty obvious.
We actually did not have different color links for visited on Super User. An oversight. I just changed this, so visited links are now lighter.
Now that you bring it up I am seeing the same behavior. Overall it doesn't bother me (I've never actually been a fan of different colors for visited links myself) too much, but I can see why it could be an annoyance to other users.
This has been very annoying for me. A lot of questions have similar titles and it is difficult to know if it is a question you've already looked at when the colors are all the same.
Most people after a certain age (usually 40-45 years) start having problems distinguishing shades of blue. Even though we all think it looks cool, with the internet community including this age group too (and increasingly, as we all get older), color schemes based on mainly shades of blue should be avoided. Especially light blue fonts on dark blue background, but also - as is the case here - similar shades of blue to distinguish properties of the content.