What does a yellow fiber optic cable mean? 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. Why are some fiber. OM1 has a 62. These are now mostly used in legacy networks or short links under 1 Gb/s or 10 Gb/s. - System level, cover protocols, signal bit rates, encoding of. Fiber optic color coding is an essential part of managing and working with fiber optic cables and components.