Update! Rascal went in to the vet for a teeth cleaning, and after looking at his nails the vet decided it was some sort of undetermined fungal/bacterial infection. So he prescribed some sort of antiseptic soak for Rascal's footsies, 5 minutes, 2 times a day, for.... 21 days. 
Anyway, he agreed it's not a huge deal, I just thought I'd post an update in case anyone else ever sees similar weirdness on the nails. I'll update with how it works after a little bit.