Rinse salmon and pat dry with paper towels. In a bowl, stir together sugar, orange peel, salt, and pepper. Place salmon in a baking dish and sprinkle with the sugar mixture. With your fingers massage the seasonings into the salmon. Cover and chill for 1 or 2 hours, up to 24.
Coat grill rack with nonstick cooking spray. Remove the salmon from its marinade and discard any accumulated liquid. Grill salmon, covered, until it flakes easily with a fork, about 14-18 minutes.
Meanwhile, prepare the salsa (it can also be prepared up to 24 hours in advance). In a bowl, combine the chopped grapefruit, raspberries, grapefruit juice, and sugar.