Yellow is the designation for single-mode fiber. The same old rule comes. But with thousands of fibers in a single cable, color coding is your universal translator. Without it, you'd be lost in a spaghetti mess of glass. When you look at a fiber optic cable, the outer jacket color instantly tells you. Outdoor fiber is a bit harder to see from the outside since it is often black with text for identification (black for UV protection), but indoor is often shown in photos on STH and the rest of the Internet. The colors typically follow a color scheme established by industry. Multimode fiber optics utilize a specific designation of OM1 through OM5 (with higher numbers representing faster cables).
