Rind and flesh color are important characteristics that are genetically controlled. Among seeded watermelons rind color patterns are referred to as Allsweet, Jubilee, Crimson Sweet, and black. Red is the most common flesh color, but orange and yellow are also available. Intensity and shade of flesh and rind color can vary among varieties. Characteristics of numerous varieties are reported in the annually published Midwest Vegetable Variety Report.
Whiteheart is a hard white streak of flesh through the heart of the watermelon. If this streak exceeds 0.25 in. (6 mm) in diameter it is classified as damage in the United States Standards for Grades; if it exceeds 0.5 in. (13 mm) it is classified as serious damage. Whiteheart is associated with excessive moisture and nitrogen during maturation.
Storage at temperatures below 50˚F reduces red color in the flesh. Temperatures above 70˚F intensify the red flesh color.