[NTG-context] parameters in startuseMPgraphic

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