Hello,
In the code below, why headcommand enough ?
thanks,
Fabrice

\setupbodyfont[pagella,11pt]

 \defineframed
       [ACFRAME]
       [width=0.5cm,
        height=0.5cm,
        background=color,
        backgroundcolor=red,
        foregroundcolor=white,
        forgroundstyle=bold,
        framecolor=red,
        ]

\defineenumeration
  [ex]
   [text=,
    distance=0.3em,
    width=fit,
    headcommand=\ACFRAME,
    %numberconversionset=ACCONVERSION,
    alternative=serried,
   ]

%\defineprocessor[ACPROCESSOR][color=white,command=\groupedcommand{}{}]
%\defineconversionset[ACCONVERSION][][ACPROCESSOR->n]

\starttext

\dorecurse {5} {
            \startex
              \input knuth
            \stopex
     }


\stoptext