Glass frogs are frogs whose pattern color is animated, slowly cycling through the entire color spectrum. Glass frogs can't be found in the pond or in the frog mart.
How to Get Glass Frogs
Breeding certain pairs of frogs may sometimes result in an unexpected Glass frog. This page previously listed some of the breeding combinations that led to Glass frogs. However, with the version 3.0.3 update of Pocket Frogs, that list is no longer valid. This page will be updated with new breeding combinations when they are found.
If you want to get a Chroma frog, see the how to get a Chroma frog page.