\setupframed[offset=2mm,

    corner=round,

    background=color,

    backgroundcolor=blue,

    foregroundcolor=yellow,

    frame=off,

    strut=no,

    align=normal, location=top, 

    width=\textwidth]

For example, is this case my \placefigure[right,nonumber,2*hang] {}{\externalfigure[ostrichhead][width=5cm]} is behind a yellow framed rectangle.