Lots of black spots on Red Eyed Tree Frog ( pic included )

[OH23]

Hey Guys and Gals,

I have have group of 4 RETF females in 24x24x18 exo with humidity of around 50% and between 75-80F. i feed half grown crix dusted with Repashy Calcium+ 3 times a week and occasional silk worms.
Just for general knowledge, i have RETFs for about 8 years and never had a single health issue other then occasional nose rub ( knock on wood ).

for a while now ( more than a year ) one of my females developed lots of tiny dark spots on her back. as you can see in the pic, she is in perfect physiological condition and behaving exactly like a plump RETF should.
She is very active at night, shed like a champ and hunts like a Tiger

I only attend to this problem now because i want to find out whats causing this, appear to be, skin problem. i normally never treat my frogs unless there is a known problem and/or deteriorate health status

I want to know if anyone can shed some light on this "problem" either from personal experience or from scientific literature source.

Thanks in advance and if anymore info or pictures needed i'd be happy to provide.