Everything else covered: the two orange circles.
Tricks of color
Same color in the shade
Which orange circle is brighter?
Neither: both circles are the same color, and so are the two gray squares under them.
Why? Like the checker shadow, your brain removes the shadow it sees, and makes the shaded circle look brighter than it is. It’s the same skill that makes a banana look yellow at noon, at sunset and under a lamp (called color constancy).
Picture: user:JunCTionS (based on source), Public domain · Wikipedia(opens in a new tab)