It depends is it a dark brown red or a dark dark red, it's brown red when your pregnant usually and for most dark deep red in the beginning of your cycle
Usually if its dark it can just be light near finish, I used to have dark and then it just disappear. But I'm not so sure by what dark you mean so I could be wrong
Explain what dark means. Is it a dark, blood red that is clotted? Is it off-colored like yellow or green tinges? Most importantly; does it itch, or smell strongly?