Hi 
I have this problem to show colors properly. I have defined color "myred",  but after \showcolor command  colors inside metapost can't be displayed.

Thanks 

\starttext

\definecolor[myred] [r=.8]

\showcolor

\startuseMPgraphic{test}

  fill fullcircle scaled 10mm withcolor \MPcolor{myred};

\stopuseMPgraphic

\midaligned{\useMPgraphic{test}}

\stoptext