It's not green
because green already has a job.
Green is responsible for the grazing grass.
The sky cannot be green if the the grass is

Why isn't it black?
It's not black
because black already has a job.
Black is responsible for the patted pavement on the ground
The sky cannot be black if the pavement already is.

Why isn't it yellow?
It's not yellow
because yellow already has a job.
Yellow is responsible for the shinning sun that brings light to the day.
The sky cannot be yellow if the sun already is.

Why isn't it white?
It's not white
because white already has a job.
White is responsible for fences to keep the crazy neighbors caged.
The sky cannot be white if fences already are.

Why isn't it red?
It's not red
because red already has a job.
Red is responsible for informing the rest of the world when to stop.
The sky cannot be red if stop signs already are.

Why is the sky blue?
It is blue
because blue needs a job too.
Blue is responsible for filling our ceiling with color.
The sky is blue.