The red color of blood comes from the hemoglobin that makes up the majority of the mass of the cell, which allows the blood cell to carry oxygen around the body. The plasma itself is a straw color when viewed under a microscope, but the hemoglobin makes up so much of the blood cell that its red color overpowers the color of the plasma. When a red blood cell is full of oxygen, the red has a scarlet tint to it, when it has released it's oxygen its more of a dark burgundy color.
The blue color of the veins that a person can see when looking at various areas of the body is due to the color of the veins themselves, not the actual blood. Blood is never blue at any point in the body, but the color of the blood coupled with the color of the veins gives the illusion that it might be blue inside the body. Red blood cells do not last forever. They do eventually wear down or use up all of their material. A normal cycle for a red blood cell is between a hundred and 120 days. New blood cells are being made in the human body, every minute of every day. There are approximately two to three million cells created per second. Blood cells are created in the bone marrow.