The Gourd Island Battle consisted of two large forces, something they knew prior to their arrival. The forces were essentially divided by skin color into white people and black people.
Of course, these weren't actual white people and black people; it was purely due to differing living environments.
The white people lived in the south where the forests were lush, and their dwelling environments were tree and ground holes, hence their skin was fairer, similar to modern humans, if not whiter.
Meanwhile, the black people lived in the north where vegetation was sparser, and they liked sunbathing, sunburning themselves to a pitch-black hue. Categorizing races by skin color was a first for Du You.
On such a small island, no bigger than a city, it was certainly dominated by one race.
Looking around, quite a number of people had a Flame Attribute in their attacks. Du You dared not use Mucus Swamp here in case it was ignited. Then it wouldn't matter who got poisoned.