Printing in multiple tones

[photoguy1000]

Hello. This may be a stupid question but I would really like some help. There is this company called Traveling Photo Booth and they able to print digital photo strips in multiple tones. For example, one side of the photo strip is color and the other side is black and white. You can see an example hereRental Includes | Photo Booth Rentals | The Traveling Photo Boothow can they do this and have it instantly print?