Step 1Rinse the halibut steaks under running water and pat them dry with paper towels. Set the fish aside.
Step 2Combine the olive oil, one-half cup grapefruit juice, thyme and garlic. Add salt and pepper to taste. Pour the mixture over the fish in a shallow glass dish. Cover and let the fish marinate 15 minutes.
Step 3Put the fish in a lightly buttered baking dish. Dot the top of the fish with 1 1/2 teaspoons butter. Bake in a 400-degree oven, basting once or twice with butter and pan juices, until the fish tests done, about 15 minutes.
Step 4While the fish is cooking, prepare the sauce. Heat 1 1/2 teaspoons of the butter in a small saucepan until melted. Stir in the minced shallot and sweat over low heat just until tender, about 1 minute. Stir in the remaining one-half cup grapefruit juice and blood orange juice and bring to a boil.
Step 5Reduce heat to a simmer and cook until the juice is reduced to one-third cup, about 20 minutes. Whisk the remaining cold butter into the sauce bit by bit until the sauce thickens slightly. Stir in the salt and pepper to taste.
Step 6When the fish is done, remove it from the oven and place it on serving plates. Sprinkle lightly with salt. Spoon the grapefruit sauce over and garnish with a sprinkle of chives.