The cams were sold in sets of 4. Set 1 was red, which had basic stitches - zigzag, scallop, arrow, and domino. This set usually came with the zigzag attachment. There were also sets that were blue, white, & yellow. Each set had different stitches.
These cams could be used on several different models of the "Singer Automatic Zigzag Attachment."
I'm not sure if the color coding was something that was original or if those were later cams... maybe done in the 1960s... as a sort of growing repertoire.