I rarely white my hair, as I usually wear a skull cap or a helmet. But that means I cannot take them off. Short hair, like crew cut, is very easy to white though. I do that on the hotter days. It also means I get to hide my thinning hair with makeup, like on those infomercials.
You must wear the prosthetic ears, even if they are covered. That goes for all elves. You also can't disguise your race by covering your ears. This means if you cover your head in a hood or a headband and someone is close enough to ask you "What do I see" you must tell them they see an elf. It doesn't mean you can't wear a hood or headband. But what self respecting elf covers his ears?
All exposed skin must be black. I think I'd give someone a pass on body hair, though you should do your eyebrows and facial hair because it looks much cooler.
Makeup tip: One of the hardest places to keep blacked is your neck. If you wear a tight turtleneck or other collar, you inevitably get a ring of pink skin, yuck. What I have found work is to wear a loose turtleneck or other collar. The makeup rubs off less and the shadows help to hide any bad spots. The shadows are your friend. Also with hats and headbands, you will often get that pinks trip where it moves. A looser hood that hangs will help this. I also designed my helmet with a brim that comes down past where the pink band develops, so even if I have one you'll never see it.
Hope this helps,
Scott