The clue was on the slip of paper that shows two columns of colored numbers 1-3: a blue 1, a gray 2 and a red 3 in the left hand column and a green 1, a blue 2 and a blue 3 in the right hand column. The other help you need is the picture on the wall with the two colorful (red-green-blue-gray) squares - or let me call them 4*4 tile matrices. First, look at the two 1's on the slip. The left hand 1 is blue, the right one is green. You have to locate the small tile in the 4*4 colorful tile matrix that's blue in the left hand big square and green in the right hand big square. You'll find only one such tile. That's the first tile you'll have to push on the all-white 4*4 button set that was behind the second laser gate you've opened. Then look at the 2's: gray in the left hand column, blue in the right hand column. So, the second button to push in the button-set is the on that's gray on the left-hand color matrix and blue in the right hand one - you'll find oinly one such tile again... And the same method applies for the third button.