Belt plate details

[Tarbicus]

With the Roman Britain room still closed at the British Museum, perhaps someone could shed some light on two belt plates as seen in this photo:

http://www.larp.com/legioxx/Belt2BM.jpg

From Legio XX's website: http://www.larp.com/legioxx/balteus.html

The middle belt plate seems to have two different surfaces? Or am I mistaken and it's just patina?

If you look closely at the plate on the right, are they red rust patches on the circle surrounding the central dome (upper left of the circle), or something else?

Thanks.