Mickey2 and Manalto are correct. Unless someone has messed with the cases, green or black is always for low shank and the pink or maroon are for slant. The oval green or rosy pink cases were later editions of the Singer buttonholer and the attachment itself was a beige colour (plastic) while the older models in the rectangular cases are made of metal. The buttonhole cams are all interchangeable. Some of the deluxe buttonholers made for the Singer Touch and Sew series in the late sixties had plastic green and biege and brown cams.