\setupcolors[state=start]
\setuppagenumber[state=stop]

\starttext

\framed[offset=overlay,width=5cm,height=1cm]
  {\clip[width=5cm,height=1cm,voffset=0pt,hoffset=0pt]
   {\blackrule[width=10cm,height=1cm,color=red]}}

\stoptext