After Image

- negative color illusion

This illusion is animated and can only be seen in XLogo. The gallery image won't produce any effect.
Focus on the central dot. The 'missing' rotating pink dot will show as green.

To New
  # set default screen, pen and turtle values
  ResetAll SetScreenSize [400 400] HideTurtle
  SetSC Black SetPC Green SetPS 1 PenUp
End

To Stamp
  Forward 150 SetPC SC Dot Pos
  Wait 14
  SetPC Magenta Dot Pos
  Back 150 Right 30
End

To Go
  New
  SetSC LightGray SetPW 7
  SetPC Black Dot Pos SetPW 30
  Forever [Stamp]
End

After Image
After Image

Procedures blue
Variables pink
Comments green
Library gray