I would do the tile surround in a solid black tile. It will go with anything and not add a "color" to deal with later.

I think black might be better. It would help the fireplace screen blend in more, plus it will highlight the mantle.

The terracotta is most likely original, but not sure if that influences your feelings. I'd probably go with a different mantle (just my two cents!) but as another option, I like the previous comment for a darker tile inside the marble. White seems to conflict with the marble to me (again, just my two cents).

I would visit the local architecture salvage places.

That is a custom carved marble mantle/surround and it is beautiful! Don't remove that! The existing tiles, while not your preference, are rather interesting and period specific. If you must replace them, please understand that proper removal of the existing tiles is the only way to do this in your historical home. It comes with some risk, but yes, it is doable (really good PRO). While we understand the reason you may have chosen the tile you are considering, we would encourage a change of direction. Keep in mind period specific choices when considering tile. There are a number tile suppliers who have lines that are period specific. Here's one that comes to mind: http://www.carreauxdunord.com/project_gallery.shtml

Our advice is to consult a tile and stone contractor/professional with experience working on fireplaces in historical homes. This isn't a DIY job anyway so begin the process of teaming with a professional who can assist.

Best of luck with your project.