Why is my leopard gecko losing his colour?

my leopard gecko is about 15 weeks old and iv had him for about a week and it seems to me that he's darker than he was when i got him, he's got a 2ft viv with a hide, come plastic plants for decoration and a heat rock and also three feeding bowls one for water, one for meal worms and one for calcium, i have been feeding him locusts which i dust with calcium dust and also have small black bugs but he doesn't eat them. his viv is at the correct Temperature and i have the lights on during the day then turn them off in the evening, so why is he going darker could he bee shedding?