In small bowl, combine first 5 ingredients; refrigerate. Peel potatoes; cut each into quarters, lengthwise. Cut each quarter into 1/4" thick slices crosswise. In large saucepan, add 2 tsp. salt to 2-qt. water; bring to a boil over high heat. Boil potato slices until crisp-tender (3-4 min.); drain. Plunge immediately into ice water; cool and drain. In large bowl, combine potatoes, eggs, celery, peppers and onion; gently fold in dressing. Refrigerate to blend flavors.