Why would an artist choose to use harmony i n a piece of art work

It can be used to stimulate and provoke. But it is mostly used to create pleasure at some level and to speak to our appreciation of color, light and texture, line, movement, balance, etc. In this painting, the artist first used a warm under-painting to establish basic harmony between the layers

is it ''blue notes? ''

hope i ! you didn't give any options so i hope that was correct! < 3

it was vincent van gogh