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Visited links on the site are a dark blue that has very low contrast with the surrounding black text. This isn't a problem in post bodies since links are dotted-underlined (except in post preview, oddly), but visited links tend to disappear in comments.
I'm a visually-typical individual, and even I have a hard time seeing a visited link when I know it's there (because I just made the comment). It won't often be a problem of course since to "disappear" a link a user has to visit it first, but some of us like to have our browsers keep our visited-link history for a very long time, and it's contrary to web design best practices to make visited links visually disappear anyway. I'm sure it's a bug or oversight (judging from the extra styling on in-post links)—could it be fixed?
A screenshot illustrates how there's hardly any contrast in luminance or colour between the regular and link text: