This tanka by Ono no Komachi is profound and notoriously difficult to translate (I like the challenge). It is layered with double meaning and wordplay, giving it layers of depth hard to capture in English.
In the first line, the flower’s color or vibrancy also has romantic or love overtones. The third line can mean in vain, or on the surface, meaning either that the author has wasted her life or modifying the next two lines so that on the surface she has grown old and lost her luster, but there is still passion on the inside. The fourth line refers to herself and says the body and the world has grown old. The fifth line can be read either as gazing or as an abbreviation for long rain. If you take the long rain meaning, it would modify “old” from the fourth line to mean “falling” as in “falling rain.”
As a result of this, different translators have tried translating it in different ways, some with a natural interpretation of the flower fading, some with an old woman thinking back on the lost beauty of her youth, some with an old woman having lost her physical beauty but still being beautiful inside. In my translation, I tried to stick to a modified literal version (except in flowing English) while trying to have the words suggest the possible interpretations without directly saying them.
The vibrant flower’s
Face has faded—
In vain I gaze
As the world grows old;
So long the rain falls.
Ono no Komachi
Hana no iro wa
Utsuri ni keri na
Wa ga yo ni furu
While vainly [could also be surfacely]
Me, the body, worldly life, gets old or falls [double meaning]
Gazing or the long rain [double meaning]