Everything covered but a diamond near the top and one near the bottom: the same.
Lighter or darker?
Cornsweet diamonds
Are the diamonds near the top darker than the ones near the bottom?
No: every row is exactly the same, shaded the same way.
Why? Each diamond is lightest at its top, just under the dark bottom of the one above. Your brain judges each one by those sharp edges, as in the Cornsweet illusion, and the edges add up differently near the top and the bottom of the picture. Checked pixel by pixel: every diamond is the same.
Picture: Drawn by Science Playground, after Tom Cornsweet · Wikipedia(opens in a new tab)