In just two lines, the speaker describes a small but real change of heart. Brown, a color most people might call plain or ordinary, was never something they thought much about, let alone loved. Then they saw her eyes, and that changed. The poem doesn't say how or why. It simply states the result, which makes the feeling seem almost too obvious to argue with.
The speaker feels admiration, and probably the first rush of being smitten. The word "never" shows how sure they once were, and "until" shows how completely that certainty fell away. The title's "her." in quotation marks, set apart like a name or a single thought, suggests she is what the whole poem is about. The mood is soft, shy, and quietly happy. There is no grand declaration here, just a plain confession that someone's eyes made an ordinary color feel special. The brevity adds to the effect, as if the speaker is so caught up that few words are needed.