Color Lab Gray Scale
Print this gray scale out on to determine values in your wool.
Punch holes in each segment, including the very bottom which is paper white and does not "show up" when printed as no ink is present.
Lay tool over wool.
Look at the holes, the one that shows up the least is the value that wool is.
In the rug hooking tradition white is #1, black is #11, with this chart we are using 11 values so we can enjoy the extremes of black and white value has to offer us.