As a bush, I say the rules apply to all. If I can wear it on my ankle, the non bushes can too. If I can hide it with my gear, they can too. Then it's a personal choice with its consequences.
I never wear it on my ankle, I'd get friendly fired too much, but I do prefer blue over red.
I do see it too many times that it is explicitly said to be an armband and non ghillies wear it on the front of their vest's shoulder strap. It's not about being in ghillie, it's about being a certain type of person.