\startuniqueMPgraphic{foo:special}
    path p ; p := unitsquare xyscaled(2cm,2cm);
    linear_shade(p,1,red,green);
    draw p withpen pencircle scaled 10;
\stopuniqueMPgraphic
\startuniqueMPgraphic{foo:nospecial}
    path p ; p := unitsquare xyscaled(2cm,2cm);
    draw p withpen pencircle scaled 10;
\stopuniqueMPgraphic

\starttext
    \startTEXpage
        \uniqueMPgraphic{foo:special}
        \uniqueMPgraphic{foo:nospecial}
    \stopTEXpage
\stoptext

