Tricky, but not impossible. If everyone took a photo with a plain grey surcoat, it wouldn't be hard to color-adjust them. I say grey, since white and black run the risk of being over or under exposed to the point of losing the fabric texture and wrinkle details. And with other colors, it can reflect on other parts of the armor. So if one person wears pink and someone else green, and then I color-adjust them all to be what we want, your eye can pick up on subtle details that are hard to fix, and thus it looks "fake".
Then again, sometimes there's a lot you can do as long as the lighting's pretty neutral.