حَمْرَاءُ (“red”, feminine) ends in a feminine alif mamdūda, represented by اء.
The word is an adjective, not a proper name. It is still a diptote because of the feminine extended-alif ending. Proper-name status is not required here.
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Recognizing Feminine Alif Mamdūda
Causes of Diptote Status — Femininity and Its Conditions
حَمْرَاءُ (“red”, feminine) ends in a feminine alif mamdūda, represented by اء.
The word is an adjective, not a proper name. It is still a diptote because of the feminine extended-alif ending. Proper-name status is not required here.