Are two different colored stools (yellowish and dark brown) normal?if bleeding is suspected, can there be partial melena and partial normal stool?

Sure...: Melena, by definition, is passage of dark stools stained with denatured blood. As we established in prior healthtap answers, all dark stool is not melena. Your doctor, or even an over-the-counter test that you can purchase, can check to see if your dark stool contains blood. Needed is for you to provide a sample of the dark stool. False positive results can occur based on diet &stool additives.