Who does not like looking up at the sky to observe clouds, the intensity of its blue, and its passing birds?  One relaxes thinking of how nice it would be to glide in the atmosphere and follow their track.  This is why, as a change to a traditional white ceiling, it is a wonderful option to introduce a sky.  It brings the outdoors, fantasy, and lightheartedness inside your home, all while adding height and depth to your room.  It can be limited to a space circumscribed around a chandelier

Banana leaves around chandelier

Or, it can be contained in a square, or inside a tray ceiling. 

Banana leaves in the sky

A tropical sky with palm or banana tree leaves adds a lot of fun, whereas a pure azure with swallows and shredded clouds accommodates a traditional or contemporary look.

Azure sky with swallows

Vertical walls provide an excellent canvas for a serene sky as well, accompanied by flying creatures or engines of your imagination: airplanes, balloons, fish, etc.  In a closed space such as an entrance, a painted sky will push back the walls; on slanted ceilings, accompanied by a trellis, it will open the roof to nature.

Bathroom with trellis.

Sky with trellis , birds and butterflies.

This is also a wonderful theme for a nursery: against this azure backdrop, trees, birds or flying engines will always look charming and amusing.

Hot air balloons on nursery walls.

 The key to a convincing sky is to keep it light to save the impression of the infinite expanse it conveys.

Light sky with birds

Sky with bird.