Diagnosing Chytrid based on skin discoloration is akin to guessing. Chytridiomycosis signs include neurological problems (abnormal behavior, posture, etc.) and rough or sloughing skin. Most of the time proper diagnosis requires veterinary analysis.

Your frogs are probably stressed out due to captivity and that is causing the discoloration and what could probably be the early stages of "Red Leg." Just in case, you might want to be prepared for that, by reading this: How to Care for a Sick Frog with Red Leg Disease: 8 Steps . Good luck !