yues keins and picasso the blue period

I recently watched a interesting program  on Pablo Picasso and Yues Keins  about their "Blue Period".

Picasso's Blue period 1901-1904

When he painted essentially monochromatic paintings in shades of blue and blue - green only occasionally warmed by other colours. These sombre works inspired in Spain but were painted in Paris, are now some of the most popular works although he had difficulty selling them at the time.  These 'Blue Period' works seemed to reflect his experience of relative poverty and instability depicting beggars, street urchins and  the old, frail, and blind.

Yues Keins  

Many of his early works were monochromes which were painted in a variety of colours, however by the late 1950's he attributed a particular role to blue.  For Keins blue embodied for him the most abstract aspects of tangible and visible nature (the sky and sea) it is said that at one time he laid on a beach a studied the blue sky.  His monochromes became almost exclusively patented as "International Klien (IKB) although the colour was never produced commercially. 

( must look into this subject further).