Ethernet cable comes in a variety of formats, grades and packages. It is possible to cut the cable raw, or cut to different lengths with connectors already installed. The wiring in the connectors can be "straight through" for regular network connections, "crossover" for computer to computer connections or "rollover" for router to console connections. These cables come in a variety of colors, including gray and blue. The color of the cable's plastic coating does not signify anything.
Ethernet is the most widely implemented set of standards for the physical properties of networks. The recommendations fall into different categories of network each delivering different performance levels. The Ethernet standards include specifications for several types of cable. However, the cheapest and most widely implemented cable type for Ethernet networks is called Unshielded Twisted Pair cable. This cable is so closely identified with the Ethernet standards that it is often called "Ethernet" cable. When computer shops sell "Ethernet cable" they are actually referring to UTP cable.
Unshielded Twisted Pair
UTP cable gets its name because there is no shield beneath the outer plastic coating of the cable. Some cables have a metal foil or woven metal sleeve surrounding the inner wires to protect them from environmental magnetic radiation. UTP does not need this because of the protective effect of its wire structure. It is called a structured cable because its eight component wires are not just bundled inside the cable, but are specially organized into pairs. The cable contains eight wires, which makes four pairs. The two wires of each pair represent the negative and positive path of a complete circuit. When a current passes along a wide it produces a magnetic field around it. Environmental magnetic interference merges with those fields. When the wires are twisted around each other, their fields combine and cancel each other out, taking away the magnetic interference with them. The lack of shield makes UTP cheaper than other cables recommended for Ethernet, which is what makes it so popular.
UTP Color Coding
The important color coding in UTP cabling is in the plastic coating around each of the inner wires. The eight wires have to be connected to eight pins of in the plugs at either end of the cable. The order in which each cable attaches to each pin is important and so color coding of the wires ensures that technicians can wire the connector correctly. Color coding of the outer plastic jacket does not signify anything.
UTP is manufactured in a variety of colors. It is up to the cabling engineer to choose which color cable to buy. The reason for producing a wide variety of jacket colors is to enable engineers to produce their own color code plan. Some implementations of local area networks can be complicated and using different colored cable for different zones of the network helps technicians keep track of the origin and purpose of each cable. A gray cable or a blue cable are exactly the same, but the color will have a meaning to the installing engineer.