Are there any Android tablets that have the "negative colours" accessiblity feature like the Samsung Galaxy S III phone has?
Yes, the Samsung Tab 3 8.0 and others. The Samsung Galaxy S III phones got this feature quite a while before it was part of the feature set of the Samsung tablets. Other Samsung tablets like the Note also appear to have this feature now, as do later versions of the Galaxy phone. I still haven't come across any other manufacturer who includes this accessibility feature with their Android tablet range.

(for any users who need high contrast to read or have a light sensitivity problem, this feature is a life saver)