Some black people's eyes yellow due to the heavy concentration of melanin in their sclera, the white part of the eye that also contributes to one's skin tone. It is the same pigment that gives some foods their color, as well. The sclera contains eumelanin and pheomelanin, which are both responsible for the eye's coloring. The combination and distribution of these pigments determines eye color.
People may also develop a yellowish tint in the sclera because of an illness or condition, most commonly liver disease. This is due to a build-up of old red blood cells in the liver, which then causes them to be deposited in the sclera. This can occur in both children and adults, but is more common in those with poor living conditions and in premature or malnourished newborns.
A yellowish sclera can also be caused by anemia, which is a low level of red blood cells that carry oxygen to the tissues of the body. There are several types of anemia, including sickle cell anemia and autoimmune hemolytic anemia, both of which can be treated with blood transfusions.
If your sclera turns yellow, or you notice any other discoloration in the white of your eyes, speak to your doctor as soon as possible. It could indicate a serious medical condition, such as a problem with the gallbladder, liver, or pancreas that is causing excess amounts of bilirubin to collect in the blood. In this case, prompt treatment is essential to prevent organ damage.