As a photography-related aside, back in the film days I found it near impossible to photograph a group of people that included both 'white' and 'black' people and get the exposure right for everyone. Yet another win for digital photography as I can take the shot in raw (just making sure I don't blow out any of the lighter parts) and I have plenty of latitude to bring up the darks enough to 'look right' on the darker faces.
Thinking about it (and using what I know about our visual system) we all do basically this automatically: as we scan the central point of our vision around (the fovea) our irises change diameter to accomodate the brightness (change exposure) - then our visual centers patch all the mini-pictures into a larger scene. So I can bring up the exposure a bit on the darker faces and it looks 'normal' - like we see with our eyes.
Having done this a bit (but as an *amateur*) I've seen a much greater variation in skin tone in 'black' people than I have in 'white'. None of this takes away from our shared humanity; just taking exposure here.