That is a good point to bring up. Walnut will be a darker grey then say birch which will be a near white light grey, osage will be a darker grey with some brown tinting to it, the longer it stays on the river bank soaking up sun and river it will turn to almost a dark chocolate grey color. Walnut will also turn to a milk chocolate grey coloring after a while. Another way to tell is by weight, osage of course would be the heaviest where walnut will come in a close second. Cedar really turns grey quickly and it doesn't change in outer color much like a medium grey, but with cedar you have "prickly" branches sticking out everywhere and with cedar the longer it is out there the darker the red becomes to an almost purple color!
