The brown pigmentation is unreliable. The slower the egg shell moves the more brown pigmentation - the quicker the egg shell travels before laying then less pigmentation. She will always be your variable egg shell color layer. I had a Marans that gave all kinds of brown pigmentation - half light/half dark shells, spotted shells, splotchy brown shells, light brown shells, all sorts of weird shades of brown or speckles or splotches and each egg looked different as if 3 different hens had layed them. Your girl's eggs will always be a surprise but I'm sure you may get an occasional green egg from her as she runs out of heavy pigmentation later in her egg-laying cycle. As long as she's healthy I wouldn't worry about egg color. I just lost my 3-yr-old Blue Wheaten Ameraucana a couple weeks ago that layed the prettiest light blue eggs but light blue eggs aren't a bonus if the chicken isn't around any more to lay them -- I'd rather still have the hen more than the blue eggs!