I'm laying unfinished tanoak and was wondering what color floor putty would work best with this wood?

For a sure color match you can use Glitsa Wood Flour Cement. You add fine edger dust from the floor being filled to the Wood Floru Cement.
If your wood changes color, the filler color will also change.
We use it on antique heart pine, brazilian cherry, brazilian walnut and other flooring that is known to change color.