According to New York Magazine:

Arriving April 1 from Stockholm, Whitelines notebooks have gray-tone pages that are cool on the eyes ($3 at Kate’s Paperie, 72 Spring St. nr. Crosby St.; 212-941-9816

See more products at the Whitelines web page.

The concept is that the white lines on grey paper is not only easy on the eyes, but will interfere less with the look of whatever you’re writing or drawing, and won’t show up on a photocopy.