explain: A condition in which the colored part of the eye (iris) is multicolored. Heterochromia iridum may be part of a genetic condition. It may also be a growth (iris nevus) or occur after an eye injury. In rare instances it may be seen with other disorders. In some cases, the color of the iris in one eye might be different from that of the other eye. For example, one eye is blue and the other brown. Heterochromia iridum is usually harmless and doesn't need treatment.