the flavor of the broth and toppings, as well as even noodle texture and thickness, is different from region to region. usually, dark brown broth made from dark soy sauce ("koikuchi shōyu") is common in eastern japan. light brown broth made from light soy sauce ("usukuchi shōyu") is common in western japan. however, many other regional types exist outside of just broth color and mainly vary in toppings used.