Thank you.

Fabrice

% macros=mkvi

\setupcolors[state=start]

\definecolor[MyColorA][c=0.00, m=0.10, y=0.20, k=0.00]

\definecolor[MyColorB][c=0.00, m=0.62, y=1.00, k=0.00]

\definecolor[MyColorC][c=0.3, m=0.00, y=0.00, k=0.05]

\definecolor[MyColorD][c=0.6, m=0.00, y=0.00, k=0.10]

\defineframedtext
[MyDefinition]
[before={\blank},
   after={\blank},
   frame=off,
   background=MyFrame,
   width=\textwidth,
   height=fit,
   location=left,
   style=italic]

\defineoverlay
[MyFrame]
[\useMPgraphic{MyFrame}]

\definelabel
[Définition]
[headstyle=\bf\smallcaps]

\startuseMPgraphic{MyFrame}
    path b ;
    picture p ;
    p := textext.rt("\white\Définition") ;
    p := p shifted (2BodyFontSize,OverlayHeight-ypart center p+.25ExHeight) ;
    b := boundingbox p leftenlarged .5EmWidth rightenlarged .5EmWidth ;
    fill OverlayBox withcolor \MPcolor{MyColorA} ;
    fill b withcolor \MPcolor{MyColorB} ;
    draw p ;