In Japanese, these are known as Sumi-e .   
(“Sumi” means “ink”, and “e” means “painting”). Sometimes I use calligraphy ink, sometimes colours.  
Like watercolour, they must have freshness and immediacy.
Not realistic, but rather something expressionistic, or impressionistic, or just fun with colour.   Eventually also a seach for the essence beneath the appearance -  a sort of Zen or Taoist approach. 

 Well, one can try!