There are a number of examples of poems that have been written based on paintings, and I think they all cast new light on the paintings themselves by forcing us to look at them and what they represent through the medium of words than art. Such poems in general force us to reconsider and re-evaluate first impressions of such paintings. For example, I would never have compared the "one black-haired tree" to a "drowned woman in the sky."
Vincent van Gogh's painting "Starry Night" is one of contrasts, contrasts that Anne Sexton's poem clearly illustrates. Against the movement of the stars, the sense of isolation that van Gogh and she have both felt, as do many artistic people, is illustrated in her lines
The town does not exist
Except where one black-haired tree slips
Up like a drowned woman into the sky.
Then, Sexton counts the stars--eleven.
The town is silent.
Anne Sexton's poem points to the isolation of the town, as well as the tree that is the poet [black-haired]. The silence of the town is certainly contrasted with the boiling night and the moon "bulging" that create movement. The yellow and blue, two complementary colors in van Gogh's painting are also in contrast to each other, like the static quality of the town.