I'm a native Arabic speaker too.
First, khadra خضراء really is the femenine form of "green". The muscular form is akhdar اخضر
Second, it really is true that we use feminine forms when referring to multiple "it"s. You probably never consciously realized it, but think about it:
beautiful flowers ازهار جميلة
beautiful girls بنات جميلات
beautiful boys اولاد جميلون
Note how jameela is the singular feminine form of the adjective.
beautiful girl بنت جميلة
beautiful boy ولد جميل
I'm a native Arabic speaker too.
First, khadra خضراء really is the femenine form of "green". The muscular form is akhdar اخضر
Second, it really is true that we use feminine forms when referring to multiple "it"s. You probably never consciously realized it, but think about it:
beautiful flowers ازهار جميلة
beautiful girls بنات جميلات
beautiful boys اولاد جميلون
Note how jameela is the singular feminine form of the adjective.
beautiful girl بنت جميلة
beautiful boy ولد جميل