Dave Bonta's short poem catches a moment most of us would call dreary and shows how vivid it actually is. The opening sets the scene plainly: heavy rain, and a sky that is one flat, gray-toned mass. Then comes the turn. Instead of dullness, the speaker says "the colors are intense," and the rest of the poem simply lists them.
Those four colors are named in a distinctive way. Laurel green, tree-trunk sable, dried-grass yellow, leaf-litter rust: each one is tied to a real thing in the landscape, so we see the color and the object together. The word "sable" feels a little rich and old-fashioned for a plain tree trunk, which makes the dark wood seem almost luxurious.
The speaker doesn't explain a feeling directly. Judging by the attention in the list, there's quiet delight, even gratitude, at noticing. The mood is calm, observant, and a little hushed, as if the rain has cleared away distraction and left only what's right in front of you.