\setupcolors[state=start]
\setuppagenumber[state=stop]

% 'frame=off' :  next frame is set to red, if its framecolor is grayscale
% 'frame=on' : next frame is ok (black)
\framed[foregroundcolor=red,frame=off]{frame should be black} % text is needed to trigger color
% wrong framecolor (red instead of black)
\framed[offset=overlay,rulethickness=1pt,framecolor=black]\bgroup
 \clip[width=5cm,height=5cm]% clip is needed
 {\externalfigure[mill.png]}\egroup

\framed[foregroundcolor=red,frame=off]{frame should be blue}
% no problem with colored frame
\framed[offset=overlay,rulethickness=1pt,framecolor=blue]\bgroup
 \clip[width=5cm,height=5cm]% clip is needed
 {\externalfigure[mill.png]}\egroup

\stoptext