For Zesty Grapefruit Mayonnaise:
Place egg substitute, half of grapefruit juice, sugar, salt and dry mustard in blender container. Cover and blend to combine thoroughly. Turn blender on high speed and slowly pour half of oil in thin stream through opening in top of blender cover. Pour in remaining grapefruit juice in thin stream, then slowly add remaining oil in thin stream. Blend until smooth and thick. Stir in grapefruit zest, place in covered container and refrigerate for at least one hour or until ready to use.
For Potato Salad:
Place potatoes, grapefruit juice, 1 tablespoon salt and enough water to cover in 4-quart saucepan. Bring to boil over high heat; reduce heat to medium and cook about 10 minutes until potatoes are tender. Drain and transfer potatoes to large bowl; toss gently with prepared Tangy Grapefruit Mayonnaise while still warm. Add grapefruit pieces, eggs, celery, green onions, parsley, salt and pepper; stir gently until combined. Cover and chill thoroughly before serving.