their are a few people who think a black diamond is a type all of its own
they have lots of little spots around the disk edge and also have spots on the underside of the disk normal leos dont normaly have spots on the underside
they are also much blacker and the spots much whiter than a normal leo
the way they change as they grow is also mad
hear is a picture of a black diamond i had then sold and a pic of how it turned out
for me they are the cream of the leos and would snap one up if i ever found one again if its a true back diamond so many people try to pass unuasally marked leos off as black diamond
75% of my leo's having marking on the belly i personally think that is not an accurate way to judge a leo, I have been told a few of mine have black diamond marking but there not really 100% diamond. I would go with what david said rows of dots along the outer disk seems to be the best way to judge.