Neither an orange nor a grapefruit!

The blood orange is a variety of orange (Citrus sinensis) with crimson, blood-colored flesh. The fruit is smaller than an average orange; its skin is usually pitted, but can be smooth. The juice is sweet but somewhat bitter and less acidic than that of regular table oranges.The distinctive dark flesh color is due to the presence of anthocyanin, a pigment common to many flowers and fruit, but uncommon in citrus fruits. Sometimes there is dark coloring on the exterior of the rind as well, depending on the variety of blood orange. The degree of coloration depends on light, temperature and variety.The blood orange is a hybrid of ancient origin, possibly between the pomelo and the tangerine. It probably originated in Sicily. - wikipedia.org