After a few hours filing through the default and a custom GUI's xml's, I found the particular bit that I needed. It seems that you must declare the definition of "title-font" in the fonts xml and give it a color and font style, otherwise that font defaults to a black color with a certain font. It was a chore to find all that because I'm not quite sure how to use TWL Themer, since it won't load anything except init.xml, and it's nothing like the outdated GUI customization tutorial, so any help with that would be appreciated.