My period blood looks black should i see a doctor immediately?

The change may be ok: If this is the very beginning or towards the end of your period & with light flow or spotting, this may be the delayed flow of residual blood in the vagina. Blood turns dark when there is a small amt of blood inhering in the vagina before flowing down. For regular to heavy constant flow of very dark menstrual blood - see your GYN doctor to examine, eval the source