There are a couple of great services out there who dynamically shifts the interface style based on contextual input, Sony Playstation XMB and Gmail to mention a few. So sure, it can definitely be pulled off without scaring off its users.
Question is though both how you do it and why you do it. You say that it's only styling and not layout that is being shifted, and yea, I would agree that this would be the 101 lesson for this behavior (that is unless of course the usage pattern for the service is greatly influenced by general contextual input/circumstances, such as shifting between landscape/portrait mode on mobile devices).
And also why you do it. Is it simply to delight the user, in the case of Gmail where the change doesn't really have any usable effect, or does it bring any function, like navigation systems switching to a darker color scheme when the surroundings are dark? If it's merely for delight, make it subtle, and iterate the design some extra turns to surely establish that the change isn't too much/obstructive.