\setupcolors
	[state=start]
\definecolor
	[shadecolor][r=.5,g=.5,b=.25] % yellow
\startuseMPgraphic{mpos:par:columnset:myunderline}
	for i=1 upto nofmultipars :
		draw bbox multipars[i] withcolor green;
	endfor ;
		draw bbox multipars[1] withcolor red;
\stopuseMPgraphic

\definecolumnset
	[example]
	[n=2]

\definetextbackground
	[underline]
	[location=text,
	 alternative=1,
	 background=,
	 frame=on]
\definestartstop
 [underline]
 [before={\starttextbackground[underline]},
  after=\stoptextbackground]

\definetextbackground
	[shade]
	[location=paragraph,
	 backgroundcolor=shadecolor,
	 mp=mpos:par:columnset:myunderline,
	 method=mpos:par:columnset,
	 leftoffset=\topskipgap,
	 before=\blank,
	 after=\blank]

\starttext
\startunderline{}\input tufte\stopunderline

\startcolumnset[example]
\dorecurse{2}
{\starttextbackground[shade]
\input tufte abcdefg
\stoptextbackground}
\stopcolumnset

\stoptext