Explanation floor 91:
Take the brush on the floor right down and keep it in your inventory menu. Tap your brush and scrub the walls right down to clean the white stains until the number "16"
Then press the number 16 to the white box on the door to the colors as shown above, which later should you change to open the door.
If you notice the color on the door would be the same result if rotated in a clockwise direction, it is an indication to open the floor 91.
Now change the colors of the squares so it looks like the following (left to right
Top row: Orange, light blue, blue
Bottom row: Green, pink, yellow
Now continue to the 100 floors level 92-93-94 explanation, or back to the 100 floors level 89-90 explanation