That works fine for this specific issue, but since posting I have found similar issues elsewhere with the dark style. 

I also found that the classic template seems to fix the issue as well, but I prefer the current template.  I'll just dig into it and apply the same solution to other areas as well.

The real underlying issue seems to be that the dark style has several poorly thought out color choices along with the default choices that can't be changed on the Colors & Styles page.  I can live with it and make it work, but it would be nice if all of the colors worked together properly.

Again, thanks for your help. 

BTW, I love your website, but my German is very rusty.  I only studied it for a year in school which was almost 50 years ago. Time to pull out the German dictionary.

Add this CSS code to the custom CSS

#wpforo #wpforo-wrap .wpforo-members .wpforo-member .wpf-members-info {
  color: #ffffff;
}

Dashboard > wpForo > Settings > Colors & Styles > Custom CSS

and clear browser cache.