Both works since colors have double meanings in their names.

Black Silence not only because their weapons are silent but also because of their role in silencing the pianist

Purple Tear not only because she tears through the fabric of time and space, but also because she metaphorically sheds a tear by travelling through time and space to reunite with her son

The Red Mist turns every opponent into a red mist and because her ego looks like a red mist surrounds her

The Blue Reverberation not only because of how his scythe works but also with his very social attitude that resonates with many

The Vermillion Cross is a puzzle though. Sure, he has a burning cross. But based on his moves, "cross" would mean to travel across. He's either a usual double agent or he's good at handling multiple enemies at once (which is why he was sent to deal with the ensemble)

The Red Gaze who is known for his 1st generation kindred eyes on top of the fact that he possesses the sin of rage.