Have you tried overprint=yes? I have that in old files which used to work
under mkii. I must admit I haven't had the need to use overprinting since
then, but I do recall that come colour handling wasn't ported across to
mkiv or later.

Duncan

On Wed, 9 Nov 2022 at 16:12, Henning Hraban Ramm via ntg-context <
ntg-context@ntg.nl> wrote:

> I’m not sure if this ever worked, but at least in latest LMTX it doesn’t:
>
> """
> \setupcolors[state=start,cmyk=yes,rgb=no,intent=overprint]
>
> \starttext
>
> \framed[
>    background=color,
>    backgroundcolor=yellow,
> ]{\ss\bfd
>    Black should always overprint.
> }
>
> \stoptext
> """
>
> The black text and frame border don’t overprint the yellow background
> but knockout. The only way to check this (that I know of) is Acrobat
> Pro’s separation simulation; the screenshot shows a snippet of the
> yellow separation.
>
> Actually, setting “overprint” for all colors doesn’t make sense, it
> should be a setting for single color (but default for black):
>
> % desired interface:
> \definecolor[overBlack][k=1,intent=overprint]
>
> Hraban
>
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