A few flags, laid over one another, left this figure. Point at them.
How to play
The figure at the top is what three of the flags below have in common (two, on easy): wherever they all carry the same colour in the same place, that colour stays printed. Everywhere else is paper.
The same colour means the very same shade. Two reds that are not the same red share nothing, so three flags with red in the middle can leave that middle as paper.
Touch the flags, or press their letters, and print. What yours have in common is printed beside the figure: comparing the two is the only clue.
You are never told how many you got right. Read the figure, rule flags out, and try again. Five tries on easy, four on normal, three on hard.