Looks reasonable for a quick effort, and if that's the main concern I don't see a problem with it.
Your girlfriend has a point in that the white doesn't show the same kind of color transition as the purple which has vivid, lighter areas of considerable size towards the top. This effect isn't there on the white which ends the transition from darker grey to white with a fairly muted, greyish look rather than actual white. If you wanted to get closer to the effect on the purple parts and tie the model's appearance together, more pure white on the top parts of armor pieces wouldn't go amiss.
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