[NTG-context] \MPcolor bug with LuaTeX

Hi, colors defined in gray values give a inverted output in MetaPost with the \MPcolor macro. The output in the text is fine and the red and cyan circles in the MetaPost graphics are also correct but the gray circle has the value s=0.1 and not s=.9 as defined in the colo-rgb file. \setupcolors[state=start] \starttext \color[gray]{Gray} \color[red]{Red} \color[cyan]{Cyan} \startMPpage fill fullcircle scaled 4cm ; fill fullcircle scaled 4cm shifted (5cm,0) withcolor \MPcolor{gray} ; fill fullcircle scaled 4cm shifted (2*5cm,0) withcolor \MPcolor{red} ; fill fullcircle scaled 4cm shifted (3*5cm,0) withcolor \MPcolor{cyan} ; \stopMPpage \stoptext Wolfgang