HI I am a (kinda) regular at these parties. I like to go there as a mare and always choose the red mask. There are many helpers there during the party who regularly come by to ask if you need something (to drink, toilet) or would like to be led outside to relax your well stretched hole. If you are wearing a white mask, the helpers also check to see that the top is wearing a rubber when penetrating you. I have always felt very safe and the helpers have always been more than helpful. I honestly think they genuinely care.
The mask is just a cloth that is wrapped around your head to ensure you can't see anything, but readily allows you to take a sniff on the popper bottle.
I hope to get back there soon. Have fun. I hope you have a good time, and get many loads!
Tino.