The mirror trick will work for this. Wrasses will display aggression that usually will fall off after three days -- that's normal. Mostly it's just chasing behaviour and as long as you have a good lid on the tank no real damage is done while they sort it out. Moving the angel out for a few days...
It depends on where it forms. If it's in the center(ish) part of the body it doesn't go away. If it's near the edges then it becomes a split and you get another one. Those "heal" as it grows out.
Don't use white. I don't know the reason why white quickly develops cyano but it always has for me, and balck never has. BRS used to carry black and shipping is free.