if the average squaddie doesn't get the word of who is wearing who, then colour doesn't really matter.
Well yeah, I agree there. But that's really irrelevant to the topic of whether plant badges were reasonable (even assuming everyone knew who was supposed to wear what).

But again, you're judging all battles in Scotland on the Culloden model
No, actually, I'm not. I don't recall mentioning Culloden, and in fact I'm thinking of battles even earlier than that. Most Highland fighting (clan warfare, where such clan affiliation would have been important) was hand-to-hand combat.

In the end, we're both speculating.
Yes, and I was pretty clear about that. I actually have no idea whether plant badges were used in the way they've been claimed. All I'm saying is that there really isn't any evidence of it until the Revival period, and it just doesn't make any logical sense to me that such a thing would have been done, given the difficulty in actually identifying plant sprigs on someone's head. I mean, what happens when a fighter loses his bonnet? That seems to happen a lot when fighting hand-to-hand. Does the whole identification system fall apart?