\startreusableMPgraphic{bullet}
    fill fullcircle
        scaled (.75EmWidth)
        withshademethod "circular"
        withcolor red shadedinto blue ;
\stopreusableMPgraphic

\definesymbol[1][\hbox{\lower.125ex\hbox{\reuseMPgraphic{bullet}}}]

\starttext

    \startitemize
    \startitem one \stopitem
    \startitem two \stopitem
    \stopitem

\stoptext

