Bright red menstrual blood is normal according to WebMD. The color of blood during menstruation varies at different times during the cycle, and bright red is most often seen during the heaviest days of flow.
Bright red bleeding during the menstrual cycle typically is nothing more than an indication of fresh blood being expelled along with the lining of the uterus. This normally occurs during the beginning of the cycle when the blood is freshest. As the cycle progresses, the blood may become darker and thicker. This is also normal.
With frequent periods, typically defined as less than 28 days apart, menstrual blood is bright red at the beginning. This is because it doesn't have time to sit in the body and become metabolized before it's expelled. Darker blood is simply older blood that has broken down in the uterus before it exits the body.
Bright red blood may also appear if there are clots being passed during the cycle. Normally, the body produces anticoagulants that help keep the blood from clotting during the menstrual cycle. However, if the cycle is heavy or faster than normal, the anticoagulants may not have time to work. When this happens, bright red blood clots might be seen. If the clots are darker in color, it simply means the blood was older when it clotted. Clotting is normally not a cause for concern, but a doctor should be consulted if the clotting is excessive.