Slice off grapefruit peels and white pith, exposing flesh. Carefully cut grapefruit segments from membranes; set aside. Squeeze 3 tablespoons juice from membranes; strain and transfer to a blender. Add egg yolk or egg substitute, vinegar, salt, pepper, paprika, and chopped vanilla bean. Purée on high until vanilla bean is thoroughly blended. With the motor running, slowly add oil. When emulsified, strain into a small bowl, discarding any tough vanilla bean debris. Refrigerate up to 1 week.