My clownfish and yellowtailed damsel don't really change color.
I think you'd be surprised at just how much they change color when the lights are out
This is perfedtly natural for these fish and many other species as well. With the green chromis inparticular alot of their color comes from the way the light reflects off their scales, if you've ever really watched them with the lights on, you noticed that they change colors depending on their angle in the tank and your angle toward them. So it relly makes sense, to me anyway, that no light equals less color for these fish.