Every wooden tube is different.  The photos will provide you an approximate color and grain pattern.  

Walnut is the darkest American hardwood. Black Walnut heartwood is rich dark brown to purplish-black and is usually straight grained. Wavy or curly grain is sometimes present. Texture is coarse.  

Each tube is made from the same board. Sawn in order, machined and a hollow hex shaped tube is glued up. The outside of the hex tube is turned to form the round tube.

Natural Walnut

Dark Walnut