A draw knife slip cut through the sapwood when I was taking the bark off, so I scraped down to the layer you see.
Having never worked with yew, I wasn't certain what was sapwood and what was heartwood. You can see the remnants of the very pale wood I removed. It was a very thin layer. I thought it might even be cambium. They back of the bow is still very light wood compared to the deep, dark wood on the belly.