The answer of quizzes
The seventh quiz
8 pieces, of course. If you watch the image to confirm it, some targets may disappear.
The sixth quiz
The rightmost reddish one. It is actually gray.
The fifth quiz
The fourth quiz
The upper one. This is the Poggendorff illusion.
The third quiz
The sixth from the left and the seventh from the top.
The second quiz
Squares c and d are the same.
The first quiz
A and C are not used. The color within each rectangle is B.