To begin with you must have completed the white retreat to the satisfactorily of your Lama, and then may be you can talk about the dark retreat.
I have had white retreats for many years. The fact is that I have only heard of dark retreat and not the yellow retreat; main thing is you must qualify to go to black retreat.
How do you know you qualify, you must be able to see in the dark. I was able to walk around in complete dark room in NYC in middle of night with no light coming from windows because of the vinyl curtains, and can still pick up small items like a small American penny on the floor if I drop them. But there are still flicker of light here and there.
The true dark retreat complete block off all light, so you really need to have your eyes able to see in the dark before you can qualified. How can you do that, you must generate light from your mind, so if anyone looked at you in the dark, you eyes would have golden light shone out of your pupils.
If you can't do that, forget about it, no one will receive you.
Vajrayana Buddhism Yogi