i have 4 different size jacks in my 90 gallon.. one is about 2 inches.. i ahve had her for about 4 months now, and only had her lighten up 2 times .rest of the time she stays black..
times she has lighten up was arly morning right when i turned the lights on the tank on..look at yours then and see if it lightens up some..
once lights are on she stays light till othe fish are awake and swmming..
so id say thats normal for that size.