I would never have believed that there was a salt water frog that looked much like a Green tree frog until I saw these little frogs in my pool the other day. I initially thought they might be cane toads until I had a closer look and noticed that they had smooth skin and spots of gold along their sides. While the pool pump hasn't been working for a couple of months (no chlorination) and we have had quite a bit of rain lately the pool is still very salty the juveniles like to sit about a metre down before they come out.
Freycinet's Blue Frog was originally discovered by Louis de Freycinet during an expedition led by D’Entrecasteaux in 1791.
The drawing here from the State Library of NSW, painted circa 1790's, looks very much like the juvenile frogs in my pool and the adults that also live near near my fathers saltwater pool.
The following link refers to a Green Tree frog that was pickled in alcohol that appeared blue as the green pigment was dissolved. These frogs have black/blue skin but are alive and kicking.
If you know anything about osmosis through semi permeable membranes you'd know that they must have quite a high concentration of salt internally to be able to survive in these conditions.