The darkening of the blood vessels on the back of the tongue is normal because the superficial blood vessels on the back of the tongue are usually venous, and the blood that travels through the veins is usually dark blue or appears to be dark black on the surface. If you are too worried, you can go to the hospital and let the doctor check. Because the blood flow in the tongue is very rich, patients should not touch it with their fingers or other hard objects or examine it by themselves to avoid causing damage to the tongue and bleeding. The blood vessels on the back of the tongue usually nourish the tongue or the face. Once a tear occurs and more bleeding occurs, you must go to the hospital as soon as possible because the bleeding and bleeding from this area can be very heavy.