Hehehe YUP! Those are stress marks and they probably got darker after that. She was probably like "Hey what gives!" LOL Beardies can't breath well on their backs so they will really struggle to not go in that direction. My vet just put my dragon in the same position though for about the same length of time and boy did Norris squirm like mad.
From what I can see your set up looks nice but if you want to go over it, we can double check it and see if something is causing her a bit of extra stress? It could just be her getting used to people and dogs, etc. Or it could be that she is getting too cold, which does make dragons darken up. Like Strangbanger said colored night lights aren't choice for bearded dragons as there is mounting evidence that it can detract from a restful night of sleep for beardies. Pet stores like to sell them in their kits and they sold me one, too, when I first got my dragon. A better night time heat source is a ceramic heat emitter or above tank radiant heat panel (expensive LOL) so most of us go with the heat emitter which just gives off heat and no light. Those black, red and blue lights are good for sneaking a peek at a animal or for a nocturnal animal but that seems to be about it.
What
UVB light are you using? Some bulbs have caused problems.
And what is your basking light? Pretty much any regular white or clear bulb will work, even regular house bulbs. For example, my dragon prefers GE Reveal indoor floodlights -60 watt as his basking light...when I say prefer, I mean that. I saw some serious stress marks when his first bulb broke and we were trying other bulbs. That was the one he finally approved of. There was one bulb that actually made him hide!! here is a link to a picture of him hiding with stress marks clear on his belly for you to see. I'm just putting the link again so I don't clutter Savanah's page with my pics. 8)
http://i134.photobucket.com/albums/q119/Mirthling/10-7mytree.jpg?t=1318096616
Of course it might not be any of these things going on and she might just be feeling a little grouchy!
-Carrie