How does Hardy use imagery in Neutral Tones to portray the state of the narrator's relationship?

Hardy wants to depict the loss of love and emotion in a relationship in the poem. The use of 'ash' to describe the tree, also evokes imagery of loss and the remnants of something that was once there. Ash itself is the burnt remains of something that was once whole, like the narrator's relationship. Alongside this is the use of colour by Hardy, as the origin of all light and life in the world, the sun, has become 'white' and lost all colour and vitality. This emphasises the lost spark and vibrance of the narrator's relationship– it is instead lifeless and dead.
Even descriptive language associated with happiness and potentially indicating some hope for the future of the narrator's relationship, is associated with death and coldness. The significant other's 'smile' was the 'deadest thing', while a grin is one of 'bitterness' rather than glee. As the first and last stanzas end with 'gray' imagery, the whole poem is metaphorically encompasses by a cold and emotionless feeling that depicts a frosty and loveless relationship