I have a quick question about the tweed fabric. I have noticed on my highland tweed trousers, as well as on an older pair of grey irish tweed pants, that there is a black line forming on the back seam of the pant. I don't know if it is from pulling or something else (though it was noticeable much sooner on the highland fabric, maybe due to the lighter color). Anyways, it is pretty obvious now, and I was wondering if it is something that can be fixed, as well as what might be the cause of it. I have attached a photo that doesn't really capture it, but hopefully suffices. I love these pants and was hoping to find an answer/solution to this issue...otherwise I fear being relegated to wearing them only with a long jacket.