While zucchini and yellow squash are both types of summer squash, they differ in color, shape and flavor. Zucchini, usually green, has a consistent width and a milder taste. Yellow squash, living up to its name, is bright yellow with a slightly swollen bottom and often has a subtly sweeter taste. Although they have slight variances in texture and flavor, they're generally interchangeable in recipes due to their similar cooking characteristics.