This has bothered me to no end as well; not a single plate armor set in the game have matching colors as a result of this. I didn’t realize until I read this post that the issue was the orientation the armor is viewed from.
Attaching my own screenshots to give a closer view of it.
As Ophanim states, when the armor is viewed from above or the front, the pieces will appear to have a different color (most notably, the chestpiece is far darker than the rest). When viewed from below, it all matches like it’s supposed to.
I reckon this is likely what caused the issues reported in this thread too:
Which means this has been an issue for over a year at least.
Edit: Actually, after viewing it in-game, the issue reported in that thread might be independent from this issue. Even when viewing the armor set in the pictures above from below, there is a stark texture / color difference between the two (and other plate sets, too).
It would be such a shame if this is never fixed. Putting cool fashion together is a big part of RPGs as far as I’m concerned; the inability to ever construct a platemail set with a uniform, static tint is a bummer.