Walnut

Creamy white sapwood, with light brown to dark chocolate brown heartwood, occasionally with a purplish cast and darker streaks. Rich patina grows more lustrous with age. Usually supplied steamed, to darken sapwood. Generally straight grained, but can have a wavy or curly grain that produces an attractive and decorative figure.

Image and description from Sierra Forest Products. 

http://www.sierrafp.com/product/category/lumber/hardwood