The Seven Deadly Sins are associated with specific colors, something frequent offenders are well aware of.

It started with a blue mask. In the game, Lu Ce was obsessed with money, valuing it over his life, and blue naturally corresponded to Greed.

Next was the red mask. In the game, Lu Ce began to eat indiscriminately, daring to consume anything, and red corresponded to Gluttony.

Anyone with some relevant knowledge and who had analyzed this strongest player could generally guess the meaning behind the color of Lu Ce's mask.