I have been on this quest many different times helping different people on 2 servers.
Originally anyone inside the tile room (stand on tile to change the color) once the puzzle was completed (tile color matches flower pattern) would be able to use lever and enter boss room, please note they each person had to use the lever before the flame other wise they are not able to enter.
I have seen 1 time, where each person had to do tile color change, I am not sure if there was something done that messed up the tile (someone mis-stepped and caused it to fail)
If it fails, you can step on tiles to reset the colors, the flower pattern can change if taken too long. Always after doing flower/tiles use the lever before the flame to make sure. If you enter flame you can exit and be placed back in previous room with team.