\setuplayout[pdftex]
\setupcolors[state=start]

\startuniqueMPgraphic{test}
  circular_shade(OverlayBox,2,red,green) ;
\stopuniqueMPgraphic

\defineoverlay[test][\uniqueMPgraphic{test}]

\starttext

\framed[background=test, width=40mm, height=20mm]{Broken}

\stoptext