When you sing in a choir, you have text and music. You rehearse and when it is time, you sing publicly in a church or a theatre. In a choir you are expected to wear the same colours in order to look and sing as one.
I read today about a choir that provides a signed translation of what is sung. The choir has a repetoire and, every other year the same music may reappear. The translator is likely to forget the texts and typically has to translate it again. The translator in the article wrote the sign language down. She does not need to remember, she knows what the text is.