So I slabbed up a few rounds I had. The Japanese walnut had lots of pin knots and insect stain similar to Rob's walnut. The willow had some color contrast, that will likely fade like other willows. These are poor cell phone pictures, so stopped after one of each.
Paul knows the crappy flip phone I have. Figured I get enough flack when not posting pics, so posted. When the rain and snow are done I'll retrieve the wood from the kiln, I mean van and use the camera for pictures.
The white sapwood tends to yellow some and the orange and pink streaks fade to a soft orangish yellow, losing the overall contrast. Happens in several of the shrub willow species. I assume it has some to do with snow loading and mico-fractures, common to many shrubs. Never found any books to site on the subject, just own experience.