The speaker describes a sky full of "little diamonds" set against "black velvet," and the poem keeps asking what that sky looks like in different light. In daytime, the diamonds are blinding, like staring into the midday sun on an open prairie. At night, the "real night," they no longer dazzle. They are almost invisible, and looking at them is like peering into a mirror in near darkness.
The poem seems to hint that the "diamonds" and "velvet canopy" are more than stars. The repeated "your" suggests the speaker is addressing someone, perhaps describing a quality in that person that shows differently depending on the moment. That is an inference, since the poem never says so directly. What comes through is admiration and steady affection. The mood is calm and reflective, with short lines like "Shining, / Sparkling, / Reflecting" slowing the pace. The ending is a promise: in every light, this will always be "your sky of diamonds."