Blackwash

[Sonia]

A wash that blackens, as opposed to whitewash; hence,
figuratively, calumny.

[Couch Potatoe]

When an established character is turned black for no reason other than to [diversify] the [cast]. It is the opposite of [whitewashing], and is normally not ever complained about

[Tanya Shivari]

To blacken the character of; to cast aspersions, disparage.