What is meant by "al-Sabr" and "yellow figs" in the context of "yellow like the yellowness of an egg, or silk, or al-Sabr, or figs"?

The characteristic of yellowness and how to distinguish it from vaginal discharge are explained in Fatwa no. 121284. As long as you can liken it to something mentioned that it resembles, this is sufficient for you to distinguish it, and it is not necessary for you to know all the things it might resemble.