In Act I, scene 3 in The Miracle Worker, which phrases helped to indicate that a flashback was taking place?
In Gibson's play, The Miracle Worker, in Act I, scene 3, stage direction indicates the onset/beginning of a flashback by describing a slight change in the stage lighting.
In fact, throughout the play, each time Annie's mind flashes to the past, there is a color change in the lighting that is used as a signal to the reader that Annie is about to remember something, which is generally a painful experience for her, reminding her of the time she spent at the poorhouse with her brother Jimmy, who eventually dies there.
During the resolution of the play, after Annie has told Helen that she loves the little girl, the lights begin to change to signal a flashback, and Annie's face reflects fear as she anticipates another painful memory. However, since she has opened her heart--to Helen, the first time she has done so since her brother's death, the moment passes without a memory, and the color of the light returns to normal.