I had the same problem while trying to identify and properly sex my Copes Greys. I did a lot of research with a lot of different sources including but not limited to internet site and recorded calls from both species and contacting the local conservation area management offices to fin out which variety are more often found in my area. After much thought, I concluded that I have 2 Cope's Grey males and a mystery female, lol. As was mention by another contributor, I don't have access to a lab and a microscope, lol. Would be nice though! I think my little girl is a Copes' too, simply because that is the most common species in my area though you can still run across a Hyala v. on occasion. They truly are amazing little frogs. My youngest male was mistaken for an ordinary green tree frog when I got him. He was always the same color (for months - almost a year actually). He was this brilliant lime green just like the green tree frogs, the only thing is he has those cheek marks just like the other 2 frogs I have Plus, no white lines on his snout, just a cute little rounded nose. But when he decide to change color for the first time, we got to see how pretty he really was. Unlike the other frogs who's patterns where outlined in a dark colored black or brown, his patterns are outlined in gold. He is so pretty, I don't think I will ever see another grey as unique as he is. I will post some pics of him when I have good lighting to show his gold rimed designs. If anyone else has seen a grey like ours please let me know. I am looking for another one a pretty as him. Thanks!