The poem sets two ways of looking at the world against each other. In the first stanza, the speaker questions who actually cares about "the foolery of fashion," which is "green and pretty as money." The comparison is sly: green is the color of nature, but here it's also the color of cash, so even the natural world seems to have been dressed up as something to sell.
The second stanza makes that sharper. We "look at nature / and home in on business," as if we can't see a forest without thinking of its value. Then the tone shifts. The last stanza turns to something certain and unbought: the owl, and "the goodness of air / so cold and so close." The speaker seems to find relief there.
The mood is quiet, a little wry, then clean and awake. The title, "Ephemera," suggests that fashion and money are passing things, while the cold air is immediate and real.