Hello,

I have solved my old question connected with preflight and overprinting of
pure text. Now I am able to have clean output, the last warning (just info)
is about the fact context files have fonts embedded like CID Type 1 fonts.

I am using this colors setup:

\definecolor[cmykblack][c=0,m=0,y=0,k=1]
\setupcolors[rgb=no,cmyk=yes,spot=yes,textcolor=cmykblack,intent=overprint]

This works well for the body. For footnotes I need to use this:

\def\numfoo#1{\startcolorintent[overprint] #1 \stopcolorintent}
\setupnotation[footnote][numbercommand=\numfoo,before={\startcolorintent[overprint]},after={\stopcolorintent}]

Just want to share that.

Honza