Most people go with the head-cannon that the armor and helmet are enchanted to change the wearers coat, tail, and mane colors. It makes sense because we mostly ever see grey and white ponies in the armor...
It might just be that the Princesses like to have conformity when it comes to the Guard. Also, I read my last reply and it kinda sounded as if I was a dick about it... Sorry if that's what you thought.
For some reason I could picture an AU where these two are partners in some sort of Men in Black/X-files-esque organization of paranormal investigators. Not that I have any idea what would be considered "paranormal" in a world like Equestria, but the sort of stuff too big for the Royal Guard to handle but not big enough to sic the Mane 6 on, and/or the sort of thing you want to keep quiet in order to avoid panic.
Are Cloud Skipper's mane and tail supposed to be different colors like that? [link] I've pulled up this pic before, but I have only just now noticed that. ...Actually, same goes for Midnight Blossom--her tail isn't the same as in [link].
I'm thinking about it, and my guess is that it was intentional on your part. Now to make sense of it--I'll wager a guess and say it's part of the armor/uniform, or the effect of an enchantment put upon the armor? Tell me if I'm right.