Arthur recognized the ugly disciples of the Purple Flower sect to be the ones who have also modified their bodies. So their ugliness is a result of their intentional cultivation.
This physical modification doesn't grant enhanced defense like that of the Blood Skull sect, but it turns the body into a natural producer of poison.
He read that every color on their body represents a different type of poison. So the more colorful their bodies are, the more poisons they have.
Arthur thought to himself solemnly, "I hear that their poison is terrifying. I should take care when I fight these kinds of people."
He doesn't think that there is anyone who can match the disciples of the Blood Skull in terms of raw power. But he also knows that raw power is not everything there is to a fight, especially when that fight is a fight to the death.
The disciples of the Purple Flower sect are masters of poison. So even though they are weak, they must not be taken lightly.
