Originally Posted by kanishou

Officially, no. Though internal support for themes still exists, and could easily be enabled with a third party GUI (or you could just make theme packages that enable themselves when installed).

Consistently changing the look of the whole device with all its applications (these days, GUIs are not just a collection of a few limited building blocks anymore), will be a lot of effort of course. On the upside, this also means that your possibilities for deep customisation are vastly increased, with application specific customisations and all.

You also have a lot more control over the actual layout of elements (if you want to go there) than you did with Fremantle customisation.