The correct answer is B.
The phrase "she turned white for just a moment” taken from this characterization of Della from "The gift of the magi" shows that Della is afraid of Jim's reaction.
Colors have always been used in stories to create concrete images of their characters, scenes and events. Turning white is a commonplace in literature used by authors to express that the characters feel fear, since, when people are afraid, they tend to go pale.