The colour shift that gives it away
A settled White's tree frog wears its brightest colours: vivid green, sometimes blue-green, with a plump, smooth-skinned look and a relaxed sprawl on a branch. Stress flips that palette. A frog that has turned dark olive, brown or muddy grey-green and stayed that way through its active evening hours is telling you something in its world is wrong. Colour alone can flicker a little with temperature and time of day, so judge it alongside the other signs rather than on its own. A frog that is dark every night, several nights running, is not moody. It is reacting to something.
Posture, hiding and a vanished appetite
Watch how the frog holds itself. A comfortable White's perches up high on a branch or against the glass, limbs tucked neatly, eyes bright and watchful once the lights dim. A stressed frog hunches low, squeezes into the darkest corner it can find, or presses flat against the substrate as if trying to disappear. It may sit in the water bowl for hours at a stretch, far beyond a normal drink and dip. Appetite is the clearest meter of all: this species is famously greedy, so a frog that turns away from food it would ordinarily snap up, two or three feeds in a row, is giving you hard evidence. Hip bones that start to show and a visible backbone confirm the picture.
What usually sets it off in a home tank
Work through the environment first, because it is the cause far more often than illness. Check that the warm end and cool end of the tank really are what the dials claim, and check humidity just after misting and again several hours later, because a tank that dries out between sprays keeps the frog in a constant low-grade struggle. Recent changes matter enormously: a new tank mate, a rearranged branch, a move to a busier room, a cat that has taken to sitting by the glass, or a spell of enthusiastic handling by visiting children. White's tree frogs tolerate gentle handling, but a week of being passed around can leave one hiding and off its food.
Putting things right
Reverse the most recent change if you can identify one, and correct any temperature or humidity reading that has drifted. Then leave the frog alone: no handling, calmer activity near the tank, and food offered in the evening without anyone hovering to watch. Stress from a setup problem usually eases within days once the cause is gone, and the bright colour and the appetite come back together. Where you can, change one thing at a time, so you learn which fix actually worked. That knowledge is worth more than the fix itself the next time the frog looks off colour.
When it stops being a wait-and-see problem
Book a reptile vet if the frog has eaten nothing for well over a week, is visibly losing weight, develops spots, sores or a dull patchy skin texture, or becomes too weak to climb and grip. Those signs reach past environmental stress toward illness or parasites, and frogs decline quietly and quickly once they start to slide. Take notes on your temperatures, humidity and the day the signs began, because a vet can do far more with a timeline than with the frog alone. A simple daily care record kept in KinsLe, with Care Teams duties marking who misted, fed and checked the frog and when, builds exactly that timeline without depending on anyone's memory.