Are all the gray squares in the checker board the same shade? Yes. If you don’t believe it drag the pill-shaped swatch over the squares to see if they really match.
Now drag the circular lens onto the checker board. The circular lens makes the colors below appear darker. Center the circular lens over any one of the white squares on the checker board.
Does the white square under the circular lens match the surrounding gray squares? It looks lighter. Is it really? Use the pill-shaped swatch to check them. Wow!
The circular lens makes the white squares appear gray, but it also makes the nearby gray squares appear black. Rule of Contrast: Light colors always tend to look lighter when they are surrounded by black.