Why there are no green coloured stars ??

 Stars emit light because they are hot.

Stars radiate heat away as light and their apparent colour depends on their temperature.

Relatively cool stars emit red light, much hotter stars glow in blue.

As stars get hotter, their colour shifts from red to orange.  As temperature rises even higher, our eyes start to interpret them as blue or white..

There is no temperature where our eyes can interpret as green   !!!