Thanks Wolfgang.
It appears my memory did some "wishful thinking" in wanting \startuseMPgraphic{name}{key=value}. Although that would have been nice.
Hans van der Meer

On 11 Apr 2016, at 14:42, Wolfgang Schuster <schuster.wolfgang@gmail.com<mailto:schuster.wolfgang@gmail.com>> wrote:

Meer, Hans van der<mailto:H.vanderMeer@uva.nl>
11. April 2016 um 10:35
I seem to remember the following variations in \startuseMPgraphic.

(1) \startuseMPgraphic{name}{comma separated list of variables}
(2) \startuseMPgraphic{name}{comma separated list of key=value pairs}
In the second case one is able to set a default value to that variable, possibly to be overridden with \useMPgraphic{name}{key=value}.
I very much would like to specify default values on the \startuseMPgraphic definition of the graphic.

However, I cannot get option (2) working. Do I have a bad memory (possible of course ;-), Has it to be done otherwise?

\startuseMPgraphic{hans}{color}
  pickup pencircle scaled 1mm;
  draw unitsquare scaled 1cm withcolor \MPvar{color};
\stopuseMPgraphic

\setupMPvariables[hans][color=red]

\starttext

\useMPgraphic{hans}

\useMPgraphic{hans}{color=blue}

\stoptext

Wolfgang