I have a friend who has an amazing ACA H&A RB. It is so pretty. I was looking at it the other day and in the direct sun light or light bulb, the stone went pretty dark- the fire was like nothing I had ever seen- but still, the stone was dark. I have seen other not as well cut diamonds that don''t do this (but not too much fire. Is this a "normal" thing? If so, why does this happen?