\setupcolors[state=start]


\startuniqueMPgraphic{Topline}
        draw (1pt,OverlayHeight-1pt)--(OverlayWidth-1pt,OverlayHeight-1pt)
        withpen pencircle scaled 2pt;
        setbounds currentpicture to OverlayBox;
\stopuniqueMPgraphic


\startuniqueMPgraphic{Diagonal}
	path p,q;
	p := unitsquare xscaled \overlaywidth yscaled \overlayheight;
	draw llcorner p -- urcorner p withpen pencircle scaled 2pt;
\stopuniqueMPgraphic

\defineoverlay[Topline][\useMPgraphic{Topline}]
\defineoverlay[Diagonal][\useMPgraphic{Diagonal}]

\starttext
\bTABLE
	\setupTABLE[r][1][background=Topline]
\bTR
   \bTD Test\ \eTD	
\eTR 
\bTR
   \bTD Test\ \eTD	
\eTR
\eTABLE

\blank
\framed[background=Topline,framecolor=red]{test}
\blank

\bTABLE
	\setupTABLE[r][1][background=Diagonal]
\bTR
   \bTD Test\ \eTD	
\eTR 
\bTR
   \bTD Test\ \eTD	
\eTR
\eTABLE

\blank
\framed[background=Diagonal]{test}
\stoptext