No, I'm not imagining it. I thought I was, at first, but I've had Tephra for over a month now and I've become quite certain that he gets darker and lighter, apparently corresponding with temperature. Even my husband noticed, and I hadn't even mentioned it to him. Tephra - so named because he looks like volcanic ash and Bolivia happens to be highly volcanic - is always a beautiful silver amarali color. But when he's colder, his silver turns very pale, almost white, especially around his face. His markings become incredibly striking as the contrast appears to increase. Then when he basks in his warm spot, after a while his face and body become darker to where they almost look dirty - the darkening is sort of speckly, like a pencil coloring lightly on paper.
I don't think I'll bother with pictures because the changes are subtle and could easily be blamed on the photography or the lighting in the cage (rest assured, I've observed these changes up close and while handling, not just in the cage). I just wanted to see if this is a known phenomenon. I know that Hog Island boas change color, but I didn't think it was possible with other species.
Teph is a pure-blood amarali from the Joe Terry line. He exhibits all the classic characteristics of this line all the way down to temperament, temperature preferences and scale counts.