Most of us discovered years ago that if you highlight the text it changes color and makes "soft colors" visible. In most browsers you can select/change what color is shown "instead of" what's posted.
The discovery was made public to many when someone tipped of the masses that "an important person involved with mudcat" had planted an invisible message at the bottom of all the threads. If you highlighted the blank space the text showed quite clearly, although it was in a place where you wouldn't even expect text.
Sadly, no such messages (at least any widely known) appear here any longer.
The method works generally, and not just at mudcat. I've occasionally run into entire web pages where the page designer used illegible color combinations that made reading extremely difficult, apparently in an attempt at being "artsy." Just "selecting" the text makes it much easier to read.