Drain the oysters in a colander over a bowl, reserving the liquid. Add enough clam juice to the oyster liquid to equal 1 cup, and set aside. Reserve the remaining clam juice for another use. Coarsely chop oysters.
Combine water and saffron in small bowl; set aside.
Melt the butter in a large saucepan over medium heat. Add the onion and celery; cook for 5 minutes, stirring frequently. Stir in flour and coriander; cook 1 minute. Add the oyster liquid, saffron water, and milk, stirring with a whisk. Cook until thick (about 12 minutes), stirring frequently. Add the oysters, parsley, salt, and pepper. Cook for 3 minutes or until edges of oysters curl.