This poem talked about the fade love of a couple. The speaker memorized how their love went away. The name of it, "Neutral Tones" had pointed out how the poem appeared. The speaker talked it with a flat tone. However, "tone" here means not only the pronunciation but also the color. There is much imagery in this poem.
In the first stanza, from the "winter day", we can imagine a bleak image. The sun was white, not as bright and shining golden as usual. Leaves fell and were gray. Gray is especially the color between black and white; it appeared the name "neutral."
In the second stanza, the riddle was a simile of the speaker. The riddles are tedious, and it also shows the attitude of the girl towards the speaker. The words between them were getting less, just like their love. He said, "some word played between us to and fro, on which lost the more by our love."
In the third stanza, the girl's face was visible. "The smile on your mouth was the deadest thing" told us the reluctation of her. What is more, "a grin of bitterness swept thereby, like an ominous bird a-wing" strongly pointed out the hypocrisy of her smile. You can get more and more knowing about their dying relationships.
In the last stanza, the speaker learnt a lesson. He started to understand the fade love, and he said, "wrings with wrong, have shaped to me." And at last, all the images were combined; "Your face, and the God-curst sun, and a tree. And a pond edged with grayish leaves." It was just like a conclusion. All imagery represented the lost love between them, bleak and withered.