Spread scallops in a single layer in a 1-2 inch deep dish.
With a paring knife or peeler, remove long strips of peel from 1 orange and 3 limes, being careful not to remove the white pith; set the peels aside. Juice the peeled fruit and the remaining orange and limes to make 1 cup of each juice; pour into a bowl. Add celery, onion, tomatoes, scallions, olive oil, ice water to the juice, then add pepper to taste and mix well. Pour over the scallops. Cover and refrigerate until the scallops are opaque, 2 to 6 hours.
Meanwhile, make the candied citrus. Place the orange and lime peels in a saucepan with water; bring to a boil and cook for 1 minute, then drain. Boil in fresh water 2 more times; drain and set aside. Combine the sugar and 1 cup water in the saucepan; bring to a boil, stirring to dissolve the sugar. Reduce heat and return the citrus peels to the pan; simmer for 45 minutes. Transfer the peels with a slotted spoon to a rack, reserving the syrup; dust lightly with granulated sugar let the peels cool, then slice into ¼-inch pieces.
Drain excess marinade from the ceviche. Add cilantro and candied citrus peels, season with salt, and toss. Transfer to a serving bowl and lightly drizzle with some of the reserved orange-lime syrup. Serve on endive leaves or with toasted bread if desired.