Offred's tone as a narrator varies throughout The Handmaid's Tale. She alternates between hope and nihilism, lost to memories of the past in response to her traumatic present.
As the primary narrator, Offred will often merge her narrative voice with those of other characters. At times, this introduces ambiguity to the question of whether or not Offred has begun to believe Gilead's propaganda. This merging of the narrator's voice with other characters' voices is called free indirect discourse (distinct from dialogue, or direct discourse, which is placed in quotation marks).
In Chapter 10, Offred uses free indirect discourse (FID) when relating a memory of Aunt Lydia. By introducing FID to this passage, Atwood makes it tonally unclear whether or not Offred actually agrees with the sentiments she's parroting:
No worry about sunburn though, said Aunt Lydia. The spectacles women used to make of themselves. Oiling themselves like roast meat on a spit, and bare backs and shoulders, on the street, in public, and legs, not even stockings on them, no wonder those things used to happen.
Offred repeats the words of "Aunt Lydia" to herself, but uses her own narrative voice instead of remembering these words as dialogue. Aunt Lydia's voice merges with Offred's, indicating that these teachings have penetrated Offred's mind as more than just a memory. Despite largely resisting propaganda, Offred falls victim to it in small ways.