[NTG-context] Using \defineoverlay for a framed text

Hello listmembers, I try to use a Metapost drawing as a background to a framed text. — I can not make it working though… \startuniqueMPgraphic{Markings} %{Markings:\overlaywidth:\overlayheight} fill OverlayBox enlarged 5mm withcolor blue; \stopuniqueMPgraphic \defineoverlay[Marks]{\useMPgraphic{Markings}} \setupframed[background=Marks] \setupframedtexts [frame=on, background=Marks] \starttext \framedtext{Hello World!} \blank \framed{Hello World!} \stoptext What is wrong with this code? Kind regards Willi