Rear sight component finishes

[RCS]

here is a photo of the rear sight on Rock Island s/n 64145 with RIA 3-07 barrel. The rear sight is without the rib on the back of the leaf, also note the early rear sight base

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[DeputyBill]

here is a photo of the rear sight on Rock Island s/n 64145 with RIA 3-07 barrel. The rear sight is without the rib on the back of the leaf, also note the early rear sight base

Thanks, RCS.
That appears to be niter blue -not color case-hardened.
Now that I think about it, maybe I'm confusing the finish with the fact that RIA rear sight bases have an "H" for "Hardened" stamped into them.