Just Listen question

In the book Just Listen Anabel and Clarke are foil characters. Foil characters are characters that are usually opposites in physicality and in their actions. One characters physicality and actions make another character's stand out because of the fact that they are complete opposites. For example, Anabel starts comparing her hair (blonde) and her eyes (blue) to Clarke's hair (brown) and to her eyes (brown "almost black"). The contrast makes there characteristics pop.
Has anyone recconized this before?