Hi Mikael,
I did not think about using Metapost, I tried with the keys of the command \framed without success.
I use the following code for my headings (thank you Aditya) and I would like to use your code instead.
Thank you.
Fabrice
\setupbackgrounds
[header]
[text]
[frame=off,
topframe=off,
bottomframe=off,
framecolor=,
rulethickness=2pt]
\defineframed
[headerframed]
[frame=off,
height=fit,
width=fit]
\definecolor[ColorA][0.8(white)]
\startsetups [headertext]
\setupheadertexts
[{\startframed [headerframed]
[foregroundstyle=bold,background=color,backgroundcolor=ColorA]
\getvariable{headertext}{title} n\high{o}\,\getvariable{headertext}{number}
\stopframed}]