\startenvironment back-0

\usemodule[simulate]

\definecolor[shadecolor][r=.5,g=.5,b=.75] % blue
\definecolor[shadecolor][r=.5,g=.5,b=.25] % yellow

\definecolor[red]  [r=.5]
\definecolor[blue] [b=.5]
\definecolor[green][g=.5]

\setuplayout
  [width=middle,height=middle,
   backspace=1cm,topspace=1cm,
   header=0pt,footer=0pt,grid=yes]

\setuprandomize
  [medium]

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

\setuptolerance
  [verytolerant,stretch]

\setupcolors
  [state=start]

\showgrid

\setrandomseed{1000}

\stopenvironment