The outer jacket color indicates the fiber's internal mode. A Yellow jacket universally signifies Single-mode fiber (OS1 or OS2), which has a 9µm core and is designed for long-distance, high-speed transmission using laser light sources. This color-coding system is standardized under TIA-598-C, making it easier for technicians and installers to identify. How to Identify Fibers in High-Count Cables (>12 Fibers) For cables with more than 12 strands (e. This color-coding standard ensures consistency, safety, and reliability throughout manufacturing, installation, and maintenance. It protects the cable from damage, bends, and moisture, and the color of that jacket actually says something important.