The vegetables gain a sweet, clean taste, like that of sushi rice, from the vinaigrette.
In a small saucepan, combine rice-wine vinegar, soy sauce, sugar, and cold water. Set over high heat, and bring to a boil. Remove pan from heat, and set rice-wine vinaigrette aside to cool.
Using a mandoline or a sharp slicing knife, julienne the carrots. Cut the bell peppers into very thin strips. Cut the bok choy on the bias into 1/2-inch-thick strips.
Fill a large high-sided skillet with 1/2 inch water. Set over high heat, and bring to a boil. Place three small steamer baskets in skillet.
Arrange carrots in one, bok choy in another, and peppers in the third. Alternatively, use one large steamer; make alternating layers of carrots and bok choy, and top with peppers. Steam vegetables until bright and tender, 3 to 4 minutes. Transfer to a serving bowl.
Drizzle the vegetables with reserved rice-wine vinaigrette, and serve.