Which part of yellow cake batter gives it the yellow cake flavor?
Yellow cake made from scratch is given its color and flavor from egg yolks. A cake mix from a box, although you didn't add any eggs to it, might already have egg product in it. If it was one of the major brands of cake mix then it will likely have additives such as flavorings and food color to give it its distinctive flavor and color. In the homemade realm a white cake is made with only egg whites and a yellow cake is made with both whites and yolk.