He's not blending in- those spots mean stress. I mean, he is blending in- spots on an animal help break it up and blend in, but for a veiled they mean he's feeling stressed about something at that moment... Probably being off of plants while having his piccy taken...
This is a simple thread but very interesting to me- I just realized after many years that the spots are not only a communication of his emotional state, but also of course spots break up an animal and cause it to blend in. So the stress response does in fact, create chamoflauge as well as serving a communication purpose to other chameleons... An appropriate response to stress...