Is there some technicality whereby one could still hold rights to illustrations and the colour of the bindings and so on.

Not sure if it applies in this case, but yes the exact typesetting is a separate copyright.

A republication of something in the public domain can be copyrighted.

Not sure why this is being downvoted because it is correct.

The product of public domain materials can be copyrighted. For example, if someone were to publish a new book of Tom Sawyer whose text is in the public domain, that book can be copyrighted. Everyone can still publish their own new books of Tom Sawyer using the public domain materials, but noone can copy that book of Tom Sawyer.

Specifically, any new creative input to the book is copyrighted. Usually, this is things like new prefaces or forewords and new illustrations or cover art.

Yep. It's one of the more important parts of copyright! Nobody will ever hear about most stuff in the public domain. Letting people benefit from hauling it out of obscurity with updates is good for the commons. Disney took it to an extreme, but I probably never would have heard of the stories they pulled from if someone didn't make hit cartoon movies based on them.