So :color: is for buttons (exception is separator).
Documentation says:
:color: Color for an indicator, can be a name or (r,g,b) values. It Is is used on buttonson indicator, "Set" buttons and separator.
Why is there not a :fontcolor: option?
Java supports it: button.setForeground(Color.RED);
From start I wanted a simple to define style for the controls. For that reason I kept settings at a minimum.
Over time some more settings has been added and helped improve the look, usually they are optional, i.e. it is still possible to define they layout in a fairly simple way.
A tag to control font color would not change that, but I do not see much reason for it, most control do not really have a good way to use a fontcolor, info and infoAsk is about the only ones where it could be used.