Much like St. Sebastian, the color orange appears twice in close succession in the poem. These echoes should set our reader's antennae twitching, as repetition is often a way that authors get us readers to, you know, Pay. Attention. But what's worth paying attention to when it comes to the color orange, anyway? In this poem, orange is a hap-hap-happy color, associated with the joy that comes with the speaker's feelings of love. It makes chromatic sense, too, as orange is a bright, warm color that wakes up our eyes and just generally cheers things up. When we see orange in this poem, we know happiness and love are there, too.
Line 3: The you of the poem is wearing an orange shirt, which makes them look like a "better happier St. Sebastian." That's some shirt. We have one Hawaiian shirt that makes us look a little bit like Magnum P.I., but that's only in certain light, and you have to squint a lot to see it. In this case, though, orange lights up the speaker's beloved and makes him beatific.
Line 5: "Fluorescent tulips"? The flowers are glowing, dude. We take this to mean that the world has taken on a new radiance in light of the speaker's love for you. This joy and energy can make everything seem brighter and more vibrant. In this case, the orange of the flowers stands out as a testament to the speaker's happiness.