AWOLF -
Jerry has raised a very valid point, indicated by the size of the tree (or log) you described. Any walnut tree that has achieved 20 inch diameter in forty years has grown exceedingly fast. It's probably safe to say that most Northeastern (Black)walnut of that girth would be approaching the century mark, unless grown on very rich bottomland in nearly ideal conditions. Slow growing trees will produce denser grain and generally darker color, though soil minerals and water will also affect coloration. One of the current ways of dealing with black walnut for sale by retailers is to have the wood steamed so that the dark heartwood extractives will bleed into the sapwood and help color it. Walnut treated this way tends to a washed out color when compared to uncompromised wood. A lot of the rich reds and purples are lost. Sapwood, on both walnut and cherry, has limited commercial value. Another instance where economics affects final product -- not necessarily to the good.
This last suggestion may be viewed as heresy, but have you considered staining your light colored walnut to a darker hue? A good dye stain (not oil stain) may help you realize good project wood. If I remember correctly, sometime this past fall/winter, there was an incredibly long thread dealing with red stains and favorite finish recipes. Walnut is walnut, though your wood may be softer or pulpy from fast growth. If it works well and holds checkering, stain it. What's the old hair dye commercial saying? "Only her hair dresser will know for sure." Or, more recently, though in another context: "Don't ask, don't tell."
