[Therion] thfill with page background colour?

[Benedikt Hallinger]

Hi metapost wizards,

I try to fill a label with the page background.
   thfill ((bbox lab)) scaled (sc * basescale * 1.5) withcolor 
<insertColorHere>;

For <insertColorHere> i tried "label_fill_color", which however may be a 
different background.
I also tried "background", but that yields the cave passage background 
colour.

In which variable do i access the page's background color (the one set 
wit the layout option "map-bg")?


Thanks!
Beni