I remember white, black, or yellow endless loop linen strings. Black had black serving, the yellow had green serving and the white could be red, green, brown, orange. There were likely many variants.
These were Bear strings that I bought at the Navy Exchange in Norfolk for my bows, and one that was on my boyfriend's Bear Grizzly. The Grizzly had the black string, the bow was a 1970.
Killdeer