The leaf color change you observed where the white-margined leaves sprout green summer leaves is called viridescence, and it's a physiological response to warm summer nights. In regions where the nights are cooler, the leaf color remains unchanged. The longer, narrower leaves produced in late summer are a normal occurrence, although it' s more prominent in this variety than in others.
Full sun tends to exacerbate the change in color and appearance.
You could force your hosta to return to its original color by cutting it down to ground level when the leaves begin to turn green. The white-margined foliage that emerges remains unchanged into the fall. If you perform this drastic operation too often, however, expect to see smaller leaves as a result. As I was taught, I pruned the crapemyrtles after the flowers withered. The following season, the three plants didn't flower, much to my disappointment.