My period color has changed from bright red to dark brown almost black. should i be concerned?

It depends: It is usually related when taking birth control pills, Depo-Provera shots or any other hormone method of contraception. But it could also be pregnancy or other irregularities in menstrual periods, like hormonal changes related with stress, thyroid problems. If this is been going on for a while you should see your primary care physician to guide you better.