When I've peaked around back, some of them do in fact have those false-color displays. I think it's like the colorful weather reports you see on the news or something; the shades correspond to the density of the material.
Note also the "aura" artifact around the barrel, which is pretty common with metals in x-ray scanners IIRC.
As for the trigger group/hammer group, I think the arrangement in the P90 has been appropriated from the AUG. The hammer and sears sit just behind the ejection chute, and a long pull wire wraps around to activate it. The safety is just a trigger block. The safe position does not allow the trigger to travel at all, semi allows it to activate the semi sears, and auto allows it to go back far enough to activate the auto sears in the auto variant. Again, IIRC, the auto trigger pull is two-stage, just like in the AUG.