Why do I get jealous over a girl even though I don't want to be with her at all?

 There are a few possible reasons why the song "The Girl from Ipanema" says the girl is "tan" instead of "tanned."

Poetic license: The song is a work of art, and the songwriter may have chosen to use the word "tan" for poetic license. The word "tan" is a single syllable, while the word "tanned" is two syllables. This makes the word "tan" more concise and easier to fit into the rhythm of the song.

Descriptive accuracy: The word "tan" can be used to describe both the color of someone's skin and the process of getting a tan. The song describes the girl as having a "golden brown" skin tone, which is characteristic of a tan. Therefore, the word "tan" is an accurate description of the girl's appearance.

Historical context: The song was written in 1962, and at that time, the word "tan" was more commonly used to describe someone's skin tone. The word "tanned" was more often used to describe the process of getting a tan.

It is also worth noting that the song is a translation of a Portuguese song, and the word "tan" may have been used in the translation because it is a more concise and direct translation of the Portuguese word "morena."

Ultimately, the reason why the song says the girl is "tan" instead of "tanned" is up to the songwriter and the interpreter to decide. However, the possible reasons discussed above provide some insight into why the word "tan" may have been chosen.