Farbenlehre
Color was different for Goethe as it was for Newton. The wheel below is his Farbenkreis of 1809: six hues, each containing its opposite. For Goethe, this was a cognitive-psychological phenomenon.
Choose a color. The complement is given. Stare at a field of that color until the page returns to paper, and the opposite effect should be produced after a few seconds.
Choose a color.
Look at the cross without shifting your gaze. The field will clear on its own.