I know how to use skinparams to change colours on lots of thnigs, but I'd like to be able to use dark colours for backgrounds (which means I want white fonts) on a case by case basis. E.g. in the following sarah works coz the color is light and black fonts work, but fred does not because I haven't found out how to color the font of the name of the group (i.e. "fred") white. The syntax I have below is what I would use to do this with an actual activity, but I can't do it on the group ... (and i'd like to be able to do it on other diagram types and containers too).
group january {
group #darkgreen:<color:white> fred {
:does x;
}
group #azure sarah {
:does y;
}
}
}