My Friend,
I can't comment on the uniform colors because I am no expert on those.
....However....
I AM a career art director, stretching back since before Photoshop was invented (for that matter, before the personal computer was invented!)
With that in mind, let me say that I think you have colorized Gen. Johnston's image in a very subtle and realistic way
and I like your approach very much! In my view, this sort of approach SHOULD be the preferred approach to projects of this nature.
Will others agree with you and me? I have no idea. I wouldn't bet on it. That's okay, too. I think a lot of viewers nowadays want to see powerful, unrealistic colors applied to these old grayscale photos. I have seen those kinds of images again and again on these threads--almost always drawing praise from the forum members.
In a way, that makes me sad. However, if that's what people want to see, then so be it.
I like your interpretation MUCH BETTER!