Thanks for your query
Cerazzette in some women can cause vaginitis
, which is inflammation of vagina. Vaginitis from any cause can produce a dark discharge. Other causes of vaginitis should also be considered like infection, non-infectious causes like spray, douches, perfumed soaps, etc.
I will also recommend that you go for a pap-smear to rule out lesions of cervix
and any infections of cervix and/or uterus
Other causes need to be ruled out by your physician. If the discharge is bad enough then I will recommend that you discuss with your physician about switching to another form of contraception
Hope I addressed your concern