Symbolism, Imagery, Allegory
Pearl has one brown eye and one blue eye. Sure, it's from some rare genetic thing, but she likes to think she can see the future with one eye. Listen to how she describes her heterochromia:
My uncle Hoyt used to tell me, when I was little, that it meant I could see fairies and peaceful ghosts. (1.1)
While Pearl can't actually see magical beings (darn), her eyes do work as a metaphor for how she sees the world. Especially when it comes to Amiel, she sees past what other people see and recognizes someone she has a strong instinctive connection to despite their surface differences.
Pearl's eyes might take up less than one-third of her face, but they're a pretty big deal. So much so, in fact, that we explore them in depth over on her page in the "Characters" section. So check it out to fully appreciate these deeps pools of symbolism.