Question

why is the light of lazor is red not another colour like yellow green etc.

Answer 1

The red colour is used in lasers because it is least scattered by the air molecules.

Answer 2

Actually the laser are of different colours. But they are mainly of red and green colours. The reason behind red being more is the wavelength of red which is more than any other colour in VIBGYOR.
Hence, it can be seen from far away easily.