This looks like an American Walnut in a character grade with a natural finish. Character grade shows more knots, grain, and variation in color. A higher grade floor would usually be color sorted for the darker colors. If you like this look you can also look at Exotic Walnut/Acacia as it is generally a bit lighter than American Walnut. The good news is character grade wood floors are generally a little less $$! Amazon Wood Floors in Los Angeles makes a beautiful Acacia engineered floor that looks similar to this.
Solaris Inc.
lindsaycr
followyourheartdesign
Paradise Flooring