\environment back-0

\startuseMPgraphic{mpos:par:columnset:shade}
  numeric h ;
  for i=1 upto nofmultipars :
    h := bbheight(p) ;
    if multikind[i] = "single" :
      fill multipars[i] topenlarged -.5h
        withshademethod "linear"
        withshadedirection shadedup
        withcolor boxfillcolor shadedinto .8white ;
      fill multipars[i] bottomenlarged -.5h
        withshademethod "linear"
        withshadedirection shadedup
        withcolor .8white shadedinto boxfillcolor ;
    elseif multikind[i] = "first" :
      fill multipars[i]
        withshademethod "linear"
        withshadedirection shadedup
        withcolor boxfillcolor shadedinto .8white ;
    elseif multikind[i] = "middle" :
      fill multipars[i] topenlarged -.5h
        withshademethod "linear"
        withshadedirection shadedup
        withcolor boxfillcolor shadedinto .8white ;
      fill multipars[i] bottomenlarged -.5h
        withshademethod "linear"
        withshadedirection shadedup
        withcolor .8white shadedinto boxfillcolor ;
    elseif multikind[i] = "last" :
      fill multipars[i]
        withshademethod "linear"
        withshadedirection shadedup
        withcolor .8white shadedinto boxfillcolor ;
    fi ;
  endfor ;
\stopuseMPgraphic

\definecolumnset
  [four]
  [n=4,
   distance=5mm]

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

\starttext

  \startcolumnset[four]

    \dorecurse{15} {
      \starttextbackground[shade]
        \simulatewords[n=10,m=500,min=1,max=5,color=text]%
      \stoptextbackground
    }

  \stopcolumnset

\stoptext