By the sounds of it your pooper may change colors from the hot and cold. If you take him out in the sun you will see the color get very dark then once in doors or a cooler spot the color will lighten up. That is from the skin absorbing all the uvb. I would say it is normal however if he starts getting yellow spots all over then it may be of something else. Hope this helps....
they can change colors pretty dramatically depending on the lighting and whether they are warm or cold as well, they can also change colors as they age after each shed, one of mine is turning out to be more yellow/orange with some red and when i got her she looked like a normal brown/tan beardie
When I take my beardie outside he gets these little bumps on his back when he is nice and warmed up. I think its cute I call them his littel goose bumps