The PVC or XLPE covering over conductor is called insulation and is provided by extrusion process only. The insulated conductor is called core. I.S. 1554 permits two types of PVC insulation TYPE A PVC compound as per I.S. 5831 which is suitable for 70 deg. C continuous operation & TYPE C PVC compound as per I.S. 5831 which is suitable for 85 deg. C continuous operation I.S. 7098 permits XLPE Insulation. The XLPE insulated heavy duty cables were introduced worldwide in mid sixties. These cables have overcome the limitations of PVC Insulations and better mechanical & electrical Properties.
The following colour code is used for identification:

Single Core : Red, Black, Yellow or Blue. Two Cores : Red and Black.

Three Cores : Red, Yellow and Blue. Three & Half: Red, Yellow, Blue and Reduced neutral Black.

Four Core: Red, Yellow, Blue and Black.

Five Core: Red, Yellow, Blue, Black, & Grey.

Six Cores: Two adjacent cores Blue and Yellow (Counting and direction core) and remaining Grey in each layer or by printing numbers on each core.