Interesting color changes

Now, I know beardies change colors slightly... Correction, they darken and lighten their original color when absorbing UV rays. This is what's puzzling me:

I will take my beardie outside with me to sit on my lap on sunny days, and he will get very noticeably darker. I'm assuming he's loving the sunshine and darkening to better take it in; he turns nearly black-backed.

However, when in his tank, I'll pick him up after he's been sitting not only 5 inches away from his UV bulb, and his face and arms will be nearly white, with his back being very light tan and an almost grey-ish blue in color.

Has his bulb stopped emitting UVA and UVB? His previous owner said I would have a good few months left, and I got him 2 months ago. It is a nearly 4-foot-long bulb, spanning the whole length of his tank. The brand and type are Reptisun 8.0. Thanks, guys!

Their color changes vary ALOT!

Though, it sounds like he is going into shed on those parts.

Also, what your asking doesnt have to do with the UVB, but just as a precaution make sure its under 6 months old, and withen 6 inches of him. :);)