Changeable Header on Any Expandable Container (Tray, Panel, Accordion...)?

Hi, all,

I would like to change appearance of a header on any expandable container element, but I can't. Here's what I have tried:

• Tray
  Tray contains a Caption as header. The Caption doesn't seem to allow appearance change and can't be replaced by some other element.
• Panel and Accordion
  These two elements only have property title and I can't see way of changing its appearance.

The element which allows change of appearance is TextView (for example, by setting design or semanticColor properties), but I don't know how (if) I can set it as a header of any expandable container element.

Is there any combination to achieve this goal?

Thanks!

KR,

Igor