Walnut with stain/dye.

Thank you!

Black Walnut heart wood with no stain and Waterlox varnish will look exactly like that. I think the sample picture is natural Walnut without stain/dye because you can see the darkness of the knot and contrast with some lighter colored grain around it. I make lots of things out of Walnut, and never use stain, making sure to carefully select all the heartwood where it will show the best color. The final result is identical to the picture.