True grapefruit cultivars do come true from seed. While most GF come true from seed, those types with pigmented flesh, but white albedos, (e.g.. Thompson seedless, Burgundy) don't. They produce seedlings which are Marsh seedless, a white GF. Those pinks and reds which have at least some blush of pink in the albedo will come true to type. (Some information in this post comes from Dr. Malcolm Manners.)