I believe the term is 'Axanthic', as in missing the xanthin or the yellow pigment. I know there are populations of Rana clamitans​ with this trait that are stable and healthy and the odd Hyla cinerea seems to pop up on the web but I've never seen a blue Barking Treefrog.

Please breed it. I'm not sure anyone bothers breeding Barkers for the pet industry, but it would probably be worth breeding blue ones and I know I'd love to have a few. I'd certainly love the chance to photograph a blue beauty like this.