TIA/EIA-568-B.1-2001 is likely the most commonly used and talked about feature of the specification created in 1988. 568-a is the definition of pin assignments for the the pairs within Category 3 (CAT3), Category 5 (CAT5) and Category 6 (CAT6) unshielded twisted-pair (UTP) cables (eight conductor, 100-ohm balanced twisted pair cabling). The Pin/Pair assignments were named T568A and T568b, both of which define the pinout or specific order the UTP pairs need to be terminated within 8P8C (Eight Position, Eight Conductor) modular connecters, also known as RJ45 connectors.
568-A Color Code
568-B Color Code