It is both a sweet and a scathing poem. It is sweet for it makes us privy to the kind of lovely conversation the poet could have with the young girl Anne Gregory. This is proof of his intimate relations with the family of Lady Gregory.
The compliment that the poet pays Anne at the end of the poem is another reason for calling it a sweet poem. Young women often suffer from insecurities about the way they look, but as the poet assures Anne, if you are a beautiful person on the inside, then you can never look ugly.
However, this poem has a somewhat hidden meaning. Rather, it would be better to say, it reveals certain stereotypes that are not generally noticed. The fact that yellow or blond hair is appealing cannot be denied. However, Anne associates other hair colours or darker hair colours with ugliness.
In young adult fiction, red haired women are often considered ugly. Moreover, in all fairy tales, witches are shown to have dark black or brown hair. These notions are put into our heads since childhood or adolescence, and hence, it is difficult not to be influenced by them.
That is perhaps why girls with dark hair or red hair always feel that they are ugly in comparison with those having blond hair. Such notions are of course reinforced by men.
Men prefer women who are conventionally beautiful rather than those whose beauty is of a different kind. They generally look only at the physical appearance of women and not at what kind of person they are on the inside.
They judge women by their looks, and so a girl who isn’t pretty but who perhaps has a great personality or some unique talent is not appreciated by her male peers in the same age group.
The poet feels that this is an injustice, and so he tells Anne to beware of men who love her for her yellow hair or for her outward appearance only. He tells her that she should only value a man who loves her for her inner beauty, even if such a man is hard to come by.