That's 100% accurate to the paint of the Vader mask in ANH which is what Lucasfilm copied when they made R1.
Also, the orbit and bridge of the nose are painted in the same dark gunmetal color, they did this so the Vader mask would show more of it's shape on film with the contrasting colors:
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I believe they did the same color variation for Vader's mask in ESB & ROTJ, but the whole helmet in those two films is a bit different; there's no widows peak on the brow of the dome and the triangular vent on his chin is larger. Also, the right side tusk is darker and appears smaller on the ANH and R1 Vader masks.
The ROTS Vader mask is very different from all of them, it's symmetrical. The shape of the actual helmet of the OT Vader masks and dome are very asymmetrical. This image of the ANH helmet shows just how asymmetrical the Original Trilogy helmet is:
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