I haven't exactly looked into whether or not it's possible to do this in the current system or not, but I have noticed from various screenshots of games that the developers seem to have gone through a whole lot of work to make the layouts flow and look pretty, and then there is always one common misfit in the design: the scrollbars. Take, for example, this screenshot of Iccusion's new Blobble interface. The scrollbar really just doesn't seem to match at all. As well, the interface to Unknown Person's Unnamed TBS Game (as I am still stubborn enough to call it.
In short, I think it would improve the overall quality of interfaces in BYOND if scrollbars could be skinned to match the rest of the design.