"Dutchman's Puzzle"—twenty-block "Pinwheel" variation

The precise and regular black-and-white pinwheels of this composition are disrupted by subtle changes in color—brown and gray are substituted here and there for black—and still more subtle shifts in pattern: look long enough, and you will see that in the second row from the top, second block from the left, one of the arms of the pinwheel is reversed.