Implantation bleeding will appear as darkish brown or pinkish in color. The blood can even be almost black due to the amount of time the blood travels in the body. The amount is typically sparse. If you are having bright blood or lots of it, it is likely not implantation bleeding.
Implantation bleeding is named as such because it is a result of a fertilized egg implanting in the uterine lining. The uterine wall is blood-rich environment. Implantation takes place roughly nine days after your body ovulates.
Sometimes a woman will experience cramping at the time of implantation. Other women do not report this experience.
If you do see what you believe to be implantation bleeding, resist the temptation to run out and buy a pregnancy test. The test is simply not sophisticated enough to pick up on the hCG levels at the point of implantation bleeding and report a pregnancy. See here when to take a pregnancy test.