The JavaDoc dark theme does currently not meet the WCAG 2 requirements for color contrast between links and normal text. One commonly suggested solution is to enable underlining of links. For JDK-8373679 the planned solution is to enable link underlining in mixed content in the dark theme only.

However, processing JavaDoc screenshots with filters that simulate impaired color vision [1] suggest that there are major issues with the default light theme as well.

[1]: https://cr.openjdk.org/~hannesw/8373679/color-sim/

It seems like a good idea to give users the option to enable underlining of links across all themes. The best way to implement this would probably be a setting in the theme switcher panel.