Question

fill in the blank question
lips have a reddish hue because of their abundant supply of superficial vessels and the reduced amount of within their outer epithelial layer.
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Explanation:

The reddish hue of lips is due to the presence of blood vessels (which contain red - colored blood) and less melanin (a pigment that can darken the skin). Blood vessels are part of the circulatory system and melanin is a substance related to skin coloration.

Answer:

blood; melanin