what are these black patches?

[UncleChester]

I've only seen dark grey but I've also seen them described as 'black'. Smaller black areas is definitely common, but the pattern of black seems messed up, so it looks like it may just a messed up colouring. The skin looks otherwise healthy from the photo.

I have also seen a Rana clamitans that was nearly jet black when it was small and as it grew it ended up with blotchy black areas like your frog. I managed to see it 3 years in a row ending up as a full sized adult so my belief was it was healthy (last picture is below). I think this falls under the 'melanistic' or 'partially melanistic' category but I don't know much about pigment defect nomenclature.