Neonatal jaundice is characterized by the accumulation of bilirubin in the blood, leading to the yellow discoloration of tissues. The yellow sclera is a hallmark clinical feature because bilirubin preferentially deposits in the sclera before the skin due to its high elastin content. This makes the yellowing of the sclera a reliable and early indicator of jaundice in newborns. Other options like blue lips, pale skin, or red rash are not specific to jaundice. Recognizing yellow sclera is essential for timely diagnosis and management of neonatal hyperbilirubinemia to prevent complications like kernicterus.

Reference: Nelson Textbook of Pediatrics, Kliegman et al., 21st Edition.