We see sun light as white because it is made up of seven colors mainly -
Red, Orange, Yellow, Green, Blue ,Indigo, Violet
these seven colors together produce the color white.
you can even experiment the newton's color test: he made a disc in which it was divided into 7 segments and colored with the seven colors i mentioned above. He rotated the disc with some speed and what he obtained was the white color. You can try the same yourself.