I used to pass (color) parameters to \startuseMPgraphic with:

\startuseMPgraphic{square}{acolor}
   draw unitsquare withcolor \MPvar{acolor}; % or \MPcolor{acolor}

In both cases I get the following error:

metapost        > initializing instance 'metafun' using format 'metafun'
metapost        > loading 'metafun' as '/Users/hansm/TeX/context-09/tex/texmf-context/metapost/context/base/metafun.mpiv' using method 'default'
metapost        > initializing number mode 'scaled'
check           > missing or ungrouped '=' after 'green' in line '7 (442>square:)'

Has something changed in this mechanism of parameter use, or am I doing something wrong?

Hans van der Meer