Usage: type /rainbow, then click anywhere in the picwin.

;BOF
alias -l drawrainbow {
  set %r 255
  set %g 15
  set %b 15
  set %y 0
  while %y != 2884 {
    inc %y
    if ( %r == 255 ) set %rfull 1
    if ( %g == 255 ) set %gfull 1
    if ( %b == 255 ) set %bfull 1
    if ( %r == 15 ) set %rfull 0
    if ( %g == 15 ) set %gfull 0
    if ( %b == 15 ) set %bfull 0
    if ( %rfull == 1 ) && (%gfull == 0 ) && (%bfull == 0) {
      inc %g 2
    }
    if ( %rfull == 1 ) && (%gfull == 1 ) && ( %bfull == 0) { 
      dec %r 2
    }
    if ( %gfull == 1 ) && (%bfull == 0 ) && (%rfull == 0) {
      inc %b 2
    }
    if ( %gfull == 1 ) && (%bfull == 1) && ( %rfull == 0) {
      dec %g 2
    }
    if ( %bfull == 1 ) && (%rfull == 0 ) && (%gfull == 0) {
      inc %r 2
    }
    if ( %bfull == 1 ) && (%rfull == 1 ) && ( %gfull == 0) {
      dec %b 2
    }
    drawline -r @rain $rgb(%r,%g,%b) 1 $calc(%y + $1) $calc(1 + $2) $calc(%y + $1) 3000 
  }
}
alias rainbow {
  window -paxdk0 @rain
}
menu @rain {
  sclick: drawrainbow $calc($mouse.x -1500) $calc($mouse.y -1500)
}
;EOF