Start by changing only the color of the circle. Observe the change in contrast between the object and the surround. By gazing at the circle, notice that the afterimage left by a previous color is added to the actual color of the current circle. The longer an area of the retina is exposed to a color, the more durable its afterimage.
Example 2a1: Object change on Green.
The circle changes from yellow to green and back.
Example 2a2: Same object change on Magenta.
How is the effect different?
Example 2a3: Three color cycle.
The circle changes: yellow to blue to green.
A penetration change occurs in the last example. The circle seems to merge with, and pass through the surround when the circle color changes from blue to green, matching the cyan of the surround for a moment.
B2b) Surround Change