Welcome to HCM,
You have not mentioned the name of contraceptives and that, whether your present bleeding is on due/expected date or not.
Sometimes blood takes more time in coming out, thus oxidize and color changes.
This is fairly common and does not indicate serious disorder.
Other causes of blackish menstruation
are extreme stress
, medicines and blood clotting.
You should please consult your Gynecologist for examination, investigations and diagnosis.
Thanks for trusting Healthcaremagic and posting your query.
Hope you found my response to your query informative and helpful.
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With good wishes,