This is a problem for people who use a dark color scheme, as in light text on dark background. The main offender is the primary text color which is normally black. However other colors such as those for Hyperlinks have been noticed as well.
This was tested with version 1.1.27.07 of AHK, as well as on Windows Vista and Windows 7.
In the example image below you can see how this may affect readability, as that color is normally on a much darker color.

This has been a problem with the help file for some years, but unfortunately I just ignored it and used the web version instead of reporting it. But when I recently updated (it had been a while) and saw the new help file setup, I figured it was time for me to stop being lazy and report the issue.