\defineviewerlayer[rotation:30]
\defineviewerlayer[rotation:60]
\defineviewerlayer[rotation:90]

\setupinteraction[state=start]

\starttext

\startTEXpage[offset=10pt]

\startMPcode
    fill fullsquare scaled 10cm rotated 30 withcolor red   withtransparency(1,.5) onlayer "rotation:30" ;
    fill fullsquare scaled 10cm rotated 60 withcolor green withtransparency(1,.5) onlayer "rotation:60" ;
    fill fullsquare scaled 10cm rotated 90 withcolor blue  withtransparency(1,.5) onlayer "rotation:90" ;
\stopMPcode

\blank[3*big] \midaligned \bgroup
    \button{Toggle 30}[ToggleLayer{rotation:30}]%
    \quad
    \button{Toggle 60}[ToggleLayer{rotation:60}]%
    \quad
    \button{Toggle 90}[ToggleLayer{rotation:90}]%
\egroup

\stopTEXpage

\stoptext
