The Identities exhibit looks to use the "brown neck" saber. Or one of them. One was auctioned.
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Then another has been used in all the reference books. I think this one is in nicer condition.
The prop that Master Replicas was given to replicate had a glossy copper neck, as opposed to brown. As far as I know, it's the only saber to have that coloration. I believe it was promotional saber.
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From the pictures we've seen. It looks like a glossy copper neck. So it's either based on that prop, based on a Master Replicas, or is a Master Replicas.
EDIT
If you couldn't tell I've been obsessing over the ROTS Obi-Wan lightsaber in the last couple of years.