[NTG-context] color in drawoptions (mplib)

hi, just encountered an expansion problem with color inside drawoptions... % engine=luatex \starttext \startuniqueMPgraphic{foo} begingroup save c ; color c[] ; c0:= red; drawoptions(withcolor c0); fill OverlayBox; endgroup; \stopuniqueMPgraphic \defineoverlay[foo][\uniqueMPgraphic{foo}] \framed[width=10cm,background=foo]{} \stoptext regards, peter