In whatever one does, always remember there’s a law guiding each deeds. Either you do good or bad, there’s surely a reward for it and there’s something called retribution. Cheng Yun should keep on turning black and keep doing what Wei Lang is teaching her, she’ll soon get her retribution.
The law of Karma
Karma says whatsoever goes around comes back around. If you do good, it’ll come back to you, and if it’s bad you choose to do, it’ll surely come back too, even in multiple folds and unexpected ways.