Can you see the reflection in the upper left corner of the piece? that's your white foam core or diffuser. It won't take much movement to get rid of that and have the color of the wood return. Just move the reflector slightly. If you play billiards you know what a bounce shot is. Look from the lens of your camera to that corner of your piece. Now imagine a pool ball following that line and bouncing up. You should see the corner of your foam core. Just move in whatever direction it takes to not bounce light from that corner back to the lens.