Yuan-Ti Pyramid

Made an underground Yuan-Ti pyramid. For the recommended atmosphere settings see screenshot. I've adjusted the light in the last pictures so you can actually see something. There is also a "secret" little cave in which you can put whatever you like.

Riddle:

Since my players scream "I have darkvision!" everytime we enter some place even mildy dark even before I finished describing it, I've decided to make a riddle where darkvision actually hinders them as you are not able to see colours with it just shades of black and grey.

There are seven snake statues in the lowest floor of the pyramid, of which all safe the center one have a crytsal sphere in their mouth. The statue in the center does have six round sockets in its body forming a triangle. As you may have guessed the riddles solution is to put the six spheres in the right sockets. But heres the trick: If they come without a light source the spheres seem the same. Only when they illuminate them will the colours become visible.
The colours and the neccessary arrangements are:
Red
Orange         Purple
Yellow          Green           Blue
To make it more interesting the snake statues fangs will bite anyone who tries to take the sphere out of their mouths and have poison gas fill the chamber after the first sphere is removed or whenever you like. Since Yuan-Ti are immun to poison they would not care about the gas nad it's just a precaution against intruders. Also if the players put the spheres in the wrong sockets the respective snake statues will come to life and attack the party. All the while the poison gas is slowly filling the room. If you want you can close the exit to this chambers to make it even more fun. After the riddle is solved the walls at the end of the chamber will slide away to reveal the treasure room.