On the right, the yellow patchcord indicates singlemode fiber and the blue connector means it is a regular PC polished connector, If it were an APC connector, it would be green. Perhaps nothing is. Since the earliest days of fiber optics, multimode cables have typically been color‑coded orange, black, or gray, while single‑mode cables are marked in yellow. This standard is defined in TIA-598-D. Put simply, tracking the different colors of the fibers, means engineers can ensure continuity. Fiber optic color codes are a standardized system under TIA/EIA-598-C that assigns each strand a color so technicians can match, splice, and trace fibers accurately. For example, the yellow fiber is often used for single-mode cables.
[pdf] 