Hello,
In this command, I have two problems :

- \currentheadnumber does not work

- the chapter number appears in black

thank you,
Fabrice

\setuppagenumbering[location=footer]

\startuseMPgraphic{head}
  pickup pencircle scaled 1mm ;
  drawoptions(withcolor lightgray) ;
  fill unitsquare scaled 1cm smoothed 1.2 ;
\stopuseMPgraphic

\defineoverlay[head][\uniqueMPgraphic{head}]

\def\Headed#1%
  {\framed
     [background=head,frame=off,offset=overlay]
     {\color[white]{#1}}}


\unexpanded\def\HeadTitle#1#2%
  {\framed
    [frame=off,
    bottomframe=on,
    width=broad,
    align={broad,nothyphenated,left}]
    {#1\blank[white]#2}}

\setuphead
   [chapter]
   [command=\HeadTitle,
    headstyle=\ss,
    numbercommand=\Headed{\currentheadnumber}]

\starttext

\startchapter
  [title={Fist chapter}]

\input knuth

\stopchapter

\startchapter
  [title={Second chapter}]

\input knuth

\stopchapter

\startchapter
  [title={Third chapter}]

\input knuth

\stopchapter

\stoptext