A grapefruit is a large, slightly tart kind of citrus fruit. The rind is mostly yellow, and often tinged with green or red. Grapefruits are categorized by the color of their pulp: red, pink, or white (which is more honey-colored than white). The color of the pulp doesn't affect the flavor. When buying grapefruit, select specimens that are smaller, thin-skinned, and heavy for their size. Some varieties are seedless. They're best in the winter and spring.