Graziani was the first to publicly comment on Leopard being a strict dominant type mutation with a homozygous that was not visually distinct from the heterozygous. He and I discussed it on ReptileRadio back in... I want to say early 2014.
Kobylka has since put out a video wherein he said that he thinks there is a very subtle difference between the heterozygous and the homozygous, at least in some of the combos he has made. The trouble there is that all the animals he showed in the video were from Leo x Leo clutches and therefore only considered possibly homozygous and to the best of my knowledge neither he not anyone else has subsequently bred them out to confirm if his supposition was correct.