Black Square is not truly black, but rather very dark purple, and has no mouth, Black Square's hyper-conscious over how he comes across to others to a potentially unhealthy degree. He desperately doesn't want to be hated or seen as boring, which can lead to him acting on impulse without thinking over the consequences of his actions. He can't talk and has a hard time expressing his feelings well, which tragically leads to him usually angering someone, even if that's not his intent.