In a large saucepan, saute the onion, celery, carrot and red pepper in butter for 5 minutes or until tender. Stir in flour until blended; gradually add milk. Bring to a boil; cook and stir for 2 minutes or until thickened. , Add the shrimp, potatoes, broth, corn, seafood seasoning and thyme. Reduce heat; cover and simmer for 10 minutes or until heated through. If desired, top with additional minced fresh thyme.