Colour is how the speaker makes sense of a crush. Blue comes first: the ink of his pen, the sound of his voice, the night sky he seems to resemble. Lying in the grass and looking up at the stars, she links his dark, bright eyes and moon-like smile to the heavens. Feeling "yellow with happiness / and blue at the same time" suggests joy mixed with sadness or longing.
Then the poem turns to gold. The boy, it seems, loves a "golden" girl, one with crimson tears and a heart full of black flowers. The speaker is brunette, yet she describes herself as having a golden soul and heart, as though she is trying on that ideal. She tries to keep her distance, but forgets in a second. The final line, "a good little golden girl," sounds both obedient and a little wistful. The mood is dreamy and tender, with an ache of unrequited feeling underneath.