Birth marks? What are the darker colored markings, lines, spots underneath the finish I see on the rod?

It is perfectly normal, do not think you have received a defective, blemished, cracked or damaged rod. Most rods are either painted or sanded prior to building to cover or remove markings, but Kistler Rods along with North Fork Composites has proven a rod that has not been sanded nor painted will perform so much better. Grab your rod and go fishing. Also, take note of your rods birth mark as a unique identification much like a serial number.