No, definitely not his eye membrane. I have had my two colonies for over a year and been around Red Eyed Tree Frogs off and on for a few decades. He's active and visiting the feeding station at night when his pupils are large as they should be and you can see the thin ring of silver around his pupil at night when it should be a thin ring of red. If I wake him during the day to check his eyes he opens his eyes fully and they look as you would expect with a slit of a pupil but the rest of the eye is a bright white/silver instead of red.