The “dark brown substance in your sperm” you noticed last year is difficult to diagnose but the “red mixed with the sperm” you notice currently might indicate blood in the sperm. You have to perform sperm analyses to confirm or exclude the presence of blood in the sperm. Blood in the sperm could be a sign of genital infection or tumor. You'll also need a physical examination of the testicles (inspection and palpation) . You can consult a urologist an schedule an appointment as soon as possible.