1Mix green beans, yellow wax beans, kidney beans, onion, celery, green bell pepper, and pimento peppers in a bowl.
2Combine vinegar, oil, sugar, salt, and pepper in a saucepan; bring to a boil. Cook and stir until sugar is dissolved, about 5 minutes. Remove saucepan from burner and pour dressing over bean mixture; toss to coat. Refrigerate until flavors blend, 8 hours to overnight.