1. Peel grapefruit, and cut into sections with a knife. Squeeze rind and remaining pulp to yield 1/4 cup juice.
2. Cook butter in a large saucepan over medium heat, stirring occasionally, 3 to 4 minutes or until it turns a golden color and smells nutty. Stir in flour; cook, whisking constantly, 1 minute. Gradually stir in grapefruit juice. Cook 1 to 2 minutes or until thickened. Stir in grapefruit segments and 1/4 teaspoon each sea salt and black pepper. Pour into a bowl; cover and keep warm.
3. Sprinkle scallops with remaining 1/4 teaspoon each sea salt and black pepper. Heat oil in a large heavy skillet over medium-high heat until hot. Add scallops, and sear 3 minutes on each side or until scallops are browned.
4. Drizzle scallops with grapefruit sauce; sprinkle with chives.