To make the marinade, combine mirin, sake, orange juice and sugar in a sauce pan. Bring to a simmer, stirring constantly until sugar is dissolved. Continue to simmer for 3-5 minutes, until the alcohol burns off.
Remove from heat and whisk in soy sauce, white and red miso paste until mixture is creamy. Set aside to cool.
When marinade is cooled, pour it into a re-sealable bag with the salmon fillets and seal. Gently massage the marinade into the salmon, coating the fish well. Marinate in the refrigerator overnight.
When ready to cook the fish, preheat oven to 350 degrees.
Take fillets out of the plastic bag and wipe off the marinade. Pat fish dry.
Heat oil in a large oven proof fry pan or skillet over medium-high heat. Sear salmon fillets 2-3 minutes on each side. Remove the pan to the oven and bake until fish is cooked through. Garnish with chives.
Cook's Note: Miso paste is available at Asian grocery and health food stores.