Final answer:
The color of the notes Mary uses is a retrieval cue, which helps her recall information from her long-term memory during exams.
Step-by-step explanation:
In the scenario described, Mary uses different colors when taking notes in her psychology class as a way to enhance her memory. When she has difficulty with a question on an exam, recalling the color of the notes relevant to that question is beneficial for her. The color of the notes serves as a retrieval cue.
Retrieval cues are stimuli that help you recall information from your long-term memory. These cues can be any kind of information that is associated with the stored information and can help in bringing that information to conscious awareness. In Mary's case, the colors are directly linked to the information she has studied, thus when she visualizes the color, it helps her retrieve the related material from her memory.