I'm by FAR no expert But I've heard of buff leaking through, ive had it happen with some of the blacks i've had.
I'm sure someone else can be more elaborate..i'm curious too!
I think it can happen. I've seen pictures of blue and lavender birds with some brown and gold around their neck. It may even go away as the adult feathers come in.
I think (from my experience) that if the feathers have started coming through a different colour you will most likely get more of them, I doubt they will just go away. I quite commonly get red leakage on lavender's as they grow up!