Hi Hans et al.,
all my greys are black:
% MWE:
\startMPpage
fill unitsquare scaled 10mm withcolor .5;
\stopMPpage
% real life example:
\startMPpage
% grayscale squares
for s=5 step 5 until 95:
numeric c; c := s/100;
fill unitsquare scaled 5mm shifted (0,(s-5)*mm) withcolor c;
label.lft(100-s, (0, (s-2.5)*mm));
endfor;
\stopMPpage
This used to work with previous LMTX versions.
Hraban