Why is the Sky Blue?

How is it that we see the sky as being blue, when air is colorless?
It s because of the dust in the air. The light of the sun Shines through the dust , which acts as a filter, allowing only blue rays of light to rise above.
But when the air is polluted with too much harmful dust , this filters the rays more than needed and the sky is no longer blue. And where pollution reaches high levels, a blue sky is only a memory.