Sure, this may be a small, straightforward poem about socks, but that doesn't mean that this is a dull, humdrum reflection. Nope. The thing is, this speaker really, really likes these socks—as the poem details for us. On top of all the metaphorical ways he thinks about them, he also finds all sorts of color in them. The vibrant, colorful imagery associated with the socks is just another way for the speaker to demonstrate his excitement about, and appreciation for, these two tootsie-warmers. Yay, socks!
Lines 21-22: The feet in these lines become lapis blue sharks. Lapis conjures up all sorts of beautiful blues, and also might make you think of the lapisphilosophorum—the philosopher's stone—which gives alchemists the power to transform minerals into gold, or, as the case may be, feet into sharks.
Lines 23-24: The sharks from the previous lines are "shot / with a golden thread." The thread reminds us that we're dealing with socks, even among all the willy-nilly transformations, and the golden color gives the socks value. Even though they're ordinary, woolen footwear, this shot of gold makes them fit for a king.
Line 25: The feet are now blackbirds, and the color-specific species makes you wonder just what color these socks are. They've gone from blue to gold to black, and all this color changing is just part of the magical transformations taking place in this poem.
Lines 32-33: The socks are called "celestial," which is a reference to the sky or the heavens, but is also the name for sky-blue in Spanish. The socks are almost like a precious jewel that changes color as the light hits it.
Lines 59-60: The gold is back! This time it's part of a birdcage made of gold. Golden cages are a common theme in poetry, and usually have to do with a rich person who is sad or bored with their riches, because they feel trapped. Here the speaker doesn't go the poor little rich girl route, and instead frees the socks from a golden doom.
Line 63: The melon in this line sounds delicious—those socks would have had a good life in the cage! But maybe the rosy pink melon flesh is a reference to another kind of flesh. Perhaps the speaker feels like he wants to save his socks for when his feet are perfectly fresh and powdered, but he knows that's not going to happen, so he sticks the stinky feet right in.