I want all visited links to have the same color
In Safari you can create a custom style sheet and import it in Safari:

E.g. in Terminal enter:

echo 'a:visited { color: red !important; }' &gt;&gt; ~/Library/Safari/link.css


Then open Safari > Preferences > Advanced > Style Sheet > Other... and choose the links.css.

In older Chrome versions you can modify the file ~/Library/Application\ Support/Google/Chrome/Default/User\ StyleSheets/Custom.css (usually a 0 Bytes file) and add the same line:

echo 'a:visited { color: red !important; }' &gt;&gt; ~/Library/Application\ Support/Google/Chrome/Default/User\ StyleSheets/Custom.css




The support for custom stylesheets has been removed in newer Chrome versions. Here I recommend an extension: Stylist.