\setuppapersize
  [S6][S6]

\language[nl]

\setuplayout
  [header=0cm,
   topspace=.2cm,
   backspace=.2cm,
   margin=0cm,
   width=fit,
   footer=1cm,
   rightedge=3cm,
   bottomdistance=5pt,
   bottom=20pt,
   height=fit]

\showframe

\definecolor [MyColor] [darkgreen]

\setupfootertexts
  [chapter][{\currentdate[month,year]}]

\setupinteraction
  [state=start,
   style=small,
   menu=on, % switching between on and off will show my problem (the vertical shift of the entire text!)!
   title=ABL File,
   author=Geert Verhaag]

\setupbackgrounds
  [page]
  [background=color,
   backgroundcolor=darkgreen]

\setupbackgrounds
  [text,header,footer][leftmargin,text,rightmargin]
  [background=color,
   backgroundcolor=white,
   backgroundoffset=.5mm]

\setupinteractionmenu
 [right]
 [background=color,
  backgroundcolor=MyColor,
  color=blue,
  frame=off,
  distance=overlay,
  unknownreference=no,
  samepage=yes]

\defineinteractionmenu
 [main][right]
 [state=start,
  width=\rightedgewidth,
  align=middle]

\startinteractionmenu[main]
  \but [inleiding]      Inleiding \\
  \vfill
  \but [CloseDocument]  sluit \\
\stopinteractionmenu

 \starttext
   \chapter[inleiding]{Inleiding}
   \dorecurse{3}{\input tufte \par \input knuth \par}
 \stoptext