Use of black
This is an important technique used to draw attention to certain areas of interest like the corners, certain parts of the trunk, outline of the bananas, shoot, stem and veins of leaves.
It is a fallacy to say that black is a colour not to be used in watercolour as it will muddy up a painting. One only needs to take care to clean brushes well and change water after using black to prevent this from happening.
Finally one stands back to compare the painting to the reference picture and examine the result.