metaobj and transparent colors with \MPcolor

["Eckhart Guthöhrlein" <eckhart.guthoehrlein@uni-bielefeld.de>]

Hi,

I try to achieve transparently filled objects using the metaobj package.
However, transparency is ignored completely in the output, I just get a
normal white. Here is my test file:

\setupcolors[state=start]
\setupbackgrounds[page][background=color,backgroundcolor=red]

\startMPenvironment[global]
  \definecolor[Durchsichtig][r=1.0,g=1.0,b=1.0,t=0.0,a=normal]
\stopMPenvironment

\startreusableMPgraphic{test}
	input metaobj;
	setObjectDefaultOption("Box")("fillcolor")(\MPcolor{Durchsichtig});
	newBox.test(btex Transparent? etex) "filled(true)";
	Obj(test).c=origin;
	drawObj(test);
\stopreusableMPgraphic

\starttext
	\reuseMPgraphic{test}
\stoptext


If I use the fillcolor as an argument to the object

	newBox.test(btex Transparent? etex) "filled(true)"
		"fillcolor(\MPcolor{Durchsichtig})";

I get error messages from the mpost run. So it seems that metaobj and
\MPcolor don't like each other.
Any ideas how to circumvent this problem?

Regards,
Eckhart