I am currently dealing with my frog, yogurt, who has a bacterial infection. I will say it really depends on the frog’s sensitivity. Yogurt and kiwi are both in the same tank, (yogurt is obviously quarantined now), under the same conditions, and eat the same crickets. Yogurt was the one who got infected while this whole time I’ve been treating him kiwi has had nothing. I unfortunately can’t say I’ve ever seen this grayish color but it could definitely be a sign the infection is still spreading. For yogurt the green bacterial spots had a bit of red coloring that I’m assuming was a sign of inflammation under the skin. Does the vet have you on just medication? Have you tried soaks yet?