TIA/EIA-568 recommends the T568A pinout for horizontal cables. This pinout's advantage is that it is compatible with the 1-pair and 2-pair USOC pinouts. The U.S. Government requires it in federal contracts.
The standard also allows the T568B pinout, as an alternative "if necessary to accommodate certain 8-pin cabling systems". This pinout matches the older AT&T 258A (Systimax) pinout. In the 1990s, when TIA/EIA-568 was published, 258A had the most widely installed UTP cabling infrastructure. Many organizations still use T568B out of inertia.
The colors of the wire pairs in the cable, in order, are: blue (for pair 1), orange, green, and brown (for pair 4). Each pair consists of one conductor of solid color and a second conductor which is white with a stripe of the other color.
The difference between the two pinouts is that the orange and green wire pairs are exchanged.