Hello what the causes of vagina become black or purpule?

I've seen such...: ...discoloration of the vagina after injury or trauma, including sexual assault, penetration by a hard object, and a blow to the crotch area (known as a "saddle injury"). If the vagina is engorged from excessive blood flow, it can have a purplish hue. The labia in some women may be darkly pigmented. Don't assume this finding is normal! See your doctor!