The speaker pictures himself as a dark silhouette against the moon’s bright face. It is an image of contrast: a shadow is usually thought of as hidden, but here the light makes it stand out sharply. The speaker lacks “color” and “vivid brightness,” yet that darkness is what gives him definition. He is not understood the way daylight is, but he is more easily seen because he stands against the light.
The mood is quiet, solitary, and a little proud. There is loneliness in being a shadow, but also clarity and self-possession. The repetition of “silhouette,” “shadow,” and “light” gives the poem a calm, almost chant-like feeling, as if the speaker is turning the idea over and slowly accepting it. In the end, being dark is not a weakness; it is what makes him distinct.