Well
What I think it is, basically if you look at something long enough without blinking and move your eyes just a little a small outline appears, in
direct opposite to the color you are looking at. Eg - there's a small trick which is black in white. It is Jesus's profile, inverted in color so
he's white and the background is black. When you stare at this long enough (say 30 seconds to 1 minute) and look at a white wall, you will see
'Jesus's profile in black. Scary huh? Not really. I think it kind of 'burns' an image onto the retina / visual cortex / area of the brain where
you see images (don't know how it works) but it does
As you said it was dark, I'm sure they were also dark and when you fractionally moved yours eyes it appeared to be 'auras' of these people. Just my
take on what you described.
Hope this helps, I'm sure there's links to this phononema... somewhere.
- Nazgarn