Do you have a physician? If you do not, I would make an appointment. Otherwise, call your physician and let them know. Darker discharge is "old" blood, blood that's been there for awhile. If it's only spotting and not "active" or "period-flow" type bleeding, that can be normal. If the spotting is accompanied with cramping, then a miscarriage needs ruled out. If you have a physician you can ask for an ultrasound to check things out and get a heartbeat. OB physicians are usually sensitive to that. But, do not worry...spotting alone is usually nothing. Let me know how things turn out for you!
Call your doctor in the morning to make sure everything is okay.
The brown and darker colors are actually what made me sigh a bit of relief for you :) I had the very same thing with my second child, it is what I was told to be residual blood, which means that is left over blood or "old" blood. which is good since it is not curent bleeding :)