Another chance is that you are viewing your mandarin either right before or after the night cycle when they take on their subdued night color but starvation is the likely cause I’m sorry.
I have noticed this as well with mine. When I turn on the lights in the morning, he is rather dull colored...but within 10-20 mins, he is back to being his bright colored self. Mine sleeps in funny spots too, I would think that he would find one of the nice nooks and crannies that I have in my LR, but he prefers to sleep on the bare spot where my maroon has shimmied away all of the LS (fun to watch...but why does he do this). It is also surprising because the maroon won't allow any other critters back there, but he leaves the mandarin alone???