It's a bicolor sponge cake because it is done with two masses. One is darker, thanks to the grated carrot and whole sugar, and the other is lighter.
Conclusion different masses and not only because of the incorporation of these two ingredients. In fact, one is made with oil and one with butter.
When carrying carrot it is best to keep the cake in the fridge, so we make sure that it is in perfect condition.
More information - Carrot cake with mascarpone and lemon glaze