Outer Layer of Hair vs. Inner Layers

I’ve only listened to a few Beauty Brains episodes, but that was enough to earn you a new fan! This is my first time posting to the forum, and my question is about hair.

I’ve recently noticed that the layers of hair underneath my outermost layer look really great– shinier, softer, wavier, darker, etc. Meanwhile, my top layer, the one everyone can see, looks dull, coarse, and frizzy. The difference is pretty dramatic. Do you have any insight as to what could account for that difference? I’m blaming brushing and sun exposure, but I really can’t be sure. If it’s relevant, my hair is long, thick, coarse, wavy, and dry. I periodically get low-lights to cover my grays.