I am 6 weeks pregnant and experiencing very dark brown almost black spotting without pain. Should I be worried?

See your OB. Although some discharge can occur with pregnancy, it is best to have this evaluated by your obstetrician as he or she may want to do additional tests to find the possible source of the discharge.
Most likely ok, but. Spotting during pregnancy is common--often due to minor bleeding as a result of repeated trauma to the more vascularized-cervix during active relations etc. If small bleeding occurs and the blood stays in the vagina cannal for long period. I.E. Overnight...The acid in vagina can turn blood dark-brown. If no other symptoms, u r likely ok. If u r still concerned, consult doc. Congrats n good luck.