color change has to do with temperature and what time of day it is and possibly how moist their skin is. my white's is very minty pearly green during the day but when he wakes up at night he changes to a dark olive green while sitting in his water dish.

as for feeding, I also put a bowl with crickets in the middle of the enclosure or sometimes take my frog out and let him eat in a different tub, this prevents him from eating any substrate. some frogs will not eat after being taken out of their cage though and spend the whole time trying to escape! I try to avoid handling my frog as much as possible though