Came across this while trying to purge an unwanted text style out of a Civil 3D template. When working with band styles for profile and section views, you can click Compose Label to set up labels along the different axes. The dialog that launches looks kind of like what you’re used to for composing labels, but there’s no General tab where you’d expect to set the text style. How does it know what text style to be?
The answer is the Summary tab of the band style. There you’ll find a setting called Band Text Style. That’s what controls the text style of the labels!
Hope that saves you some time day!

That’s the same thing that is shown on the top left of the Band Details Tab of the Profile Band Style Dialogue, as shown in your first picture, The drop down that has the title “Text Style”.
Aha! I had assumed that to be the text style for the Title only, but you’re right…that controls the whole thing. Thanks!
Thanks for the tip. I need some help with a similar issue. On the Display tab of a Profile Data style (or Vertical Geo style or Horiz Geo Style…) under Band styles, the text controls are all greyed out except for the on/off. We use .stb plotting styles and I am trying to shade the existing text, but without success. Any suggestions would be greatly appreciated. Thanks!