Paint me blue

So, it's time for traditional art! It took me some time to figure I should feature it but I made it in time ^^
It's as hard as with every kind of art - what exactly should I look for? So this time the subject is the colour. However, blue is not only a colour.

From Cambridge Dictionary:
blue
adjective (colour) of the colour of the sky without clouds on a bright day, or a darker or lighter type of this
adjective (sad) [after verb] informal feeling or showing sadness
blue-sky
adjective [before noun] using the imagination to think of ideas that do not yet have practical uses or make money //blue-sky research //blue-sky thinking

Blue Feature