How does pink grapefruit get its colour?

Pink grapefruit gets its color from a carotenoid (natural, unsaturated hydrocarbon pigment synthesized by plants) called Lycopene: Lycopene is present in many plants (tomatoes, guava, watermelon etc) and helps absorb light during photosynthesis, and confers antioxidant protection. read more

The flesh is segmented and acidic, varying in color depending on the cultivars, which include white, pink, and red pulps of varying sweetness (generally, the redder varieties are the sweetest). The 1929 U.S. Ruby Red (of the Redblush variety) has the first grapefruit patent. read more

grapefruit nutrition facts and information EDIT: The color comes from lycopene (same compound found in watermelons, tomatoes, and pink guavas), and not from beta-carotene, but I believe there is some beta-carotene as well, as the link above shows. read more