The CCB system provides a pre-planned and standardized system of connecting customer's telephone facilities to central office cables. Color coding provides a visual identification of telephone circuit classifications. Backboard Color Code Identification - Backboard Used to Terminate: BLUE Connector cables toward customer's Key Telephone Sets, GREEN Cables toward the Central Office, RED Cables or lines to and from Key Telephone Equipment, PURPLE Cables or lines to and from PBX Equipment, YELLOW Cables or lines to and from Special Services Equipment, WHITE Special Backboard for routing cross connecting runs between GB183 Type Backboards