I've done some veining with a larger spiral blade so it will stand out. You might consider filling the veining with a light color polymer clay and baking, then sanding, it. If you use black walnut for the blank then you'll get a very dark color w/o paint, especially if you burn the walnut in the oven while baking the clay. You can get exotic plywood including walnut, or add a walnut veneer on BB Ply before you cut.