It could be just that you weren't looking for it before, Vraciu noticed it on another of my skins a while back.
The original metal colour I used was RGB 122/122/135, so basically a blue tinted medium grey. Even with brown dirt layers on top the metal areas were not shifted towards red when I used a colour picker in Paint Shop Pro. So if your base metal colour also has red and green equally balanced then I'd expect a similar result to mine in the game. The second revision to my metal colour is now RGB 119/125/134, the very slight greenish tint looks a little odd in PSP but it disappears in the game.