The sky is blue, when looking from below. That's based on scattering, no problem with that: Why is the sky blue?
But it is also colorless transparent from above. No problem with that either, we look straight to the ground, there is only air in between.
So it has a color, and no color, at the same time. That is surprising!
Independent of color, that it is colored from only one side is strange. It is not opake blue from below, as we can see the sun.
That reminds of a half transparent mirror. It's not the same, as a mirror creates reflection, not scattering.
The blue color is created by scattering. Shouldn't scattering go to all directions?
How can the sky have two colors at the same time?