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Look at this: How is sushi supposed to be eaten?, there is one hyperlink in the entire answer. If you can see it, your eyes are better than mine (which wouldn't take much).
They used to be red or orange, right? Or am I just getting very blind?
The link is there, and it is a brownish-reddish-orange after being clicked. Not a very high contrast, but it is visible, and even better visible for people who haven't been there and clicked it yet.
This is a blown up version of the link after it has been clicked.