Here´s the answer

April 26, 2020   photos  

 Because black colour consume /attract the heat so we can easy move the cable when the cable become hot that's why it's colour is black. Not necessary, it depends on the application where the cable is required. Some fire resistant cables have red outet jackets that is fire resistant materials. Probably also the LSOH" low smoke zero halogen " cables are red outer jackets. The XLPE and regular PVC cables are black. Any circuit's black wire should be considered hot or live. Black wire is never used for a ground or neutral wire and should be used as the power feed for a switch or an outlet. A black wire is often used in a circuit as a switch leg, the connection that runs from the switch to the electrical load.