Not necessarily stressed. They do it when fired up, or when excited about being fed. Most keep the spots to some degree when at rest. As the cham matures the more pronounced the spots become. (veileds of course)
If your cham is a female and is about 9 months and a veiled and last but not least the spots are pretty robins egg blue, it very well could mean she is receptive.
Depending on the species and the color of the dots it could mean that the chameleon is stressed...or if its a female, it could mean that its receptive or gravid.