Wrong perception
"We can't enter the colosseum looking like our true selves. It would be best to hide our identity too. There are many humanoid races. Simple masks shall serve the purpose!"
Jason wanted them to refrain from exposing themselves before the liberation tournament.
If he were to be honest, it would be best if they could hide most of their affinities too, and only fight with one, imitating one of the other races.
By using several affinities that were normally not compatible with each other, they would only attract suspicion, which was something they had to avoid at all costs.
His own situation was slightly different because he had a stigma, and the Celestia aura, making it 'impossible' for him to pass on as an ordinary human.
Rather, others would suspect him to be a spy or a troublemaker if he were to enter the colosseum.
As such, hiding his stigma was the bare minimum he ought to do.