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

\startuniqueMPgraphic{FOO}
    fill unitsquare xyscaled(10,10) withcolor lightgray;
\stopuniqueMPgraphic


\starttext

\vbox{\normaloffinterlineskip
  \vskip5px
  \uniqueMPgraphic{FOO}
  \vskip5px}

\stoptext