By default any of the styling properties (font size, color, text transform, etc.) that you assign to a combo box will also be applied both to the list of choices and to the input box. If this option is set to false, the style properties will only apply to the input box.
pui["add combo style properties to choice list"] = false;
Where do you save this configuration option? Here.
This configuration option requires Profound UI 6 fix pack 19.