Question

why the clouds are generally white in colour ?

Answer 1

When clouds do not contain water molecules they appear white as because light rays can penetrate into the cloud and so it appear white.

Answer 2

Clouds  are  white  bcause  their  ice  crystals  or  water  droplets  are  large  enough  to  scatter  the  light  of  seven  wavelenghts  which  combine  into  white  light.(Red,orange,yellow,green,blue,indigo,violet)