How can I fix this?
Hmmm. It's not like that here and we use the same theme. Odd. Do you recall changing any settings in the serenity theme? It allows you to choose various colors. Any changes done to the CSS either?
No, I don't remember making changes to it. Where can I find the CSS for the text color?
You can edit it in your custom theme in the Appearance > Theme Editor and choose Theme.Css. Once there, and working in a clone, this is the code for the forum section you show:
ul.forum_topics .forum_topics_title h3 > a {
color: #03598F;
}
That is the default color it should be. You can change it to any color you prefer.