i think there is a simple way.
You can create a image, like 1x1px, 1 pixel darker and i pixel lighter, and apply this texture to a prite with linear filter. in this case you create a gray like sky.
After that you can color the sky by .setColor of the sprite an so you have a different sky in different time of a day.
If you want animate it you can simple use Tween manager for animation, and set the color of the sprite to animate, so you don't have to calculate the phase of the day, but only create a repeatyoyo loop animation that pass from day to night and viceversa.
I hope my explanation is pretty simple to understand