Is methemoglobinemia inherited?

Most of the time not. Methemoglobinemia aka "blue man disease" (blood has a blue tint instead of red) is due to excessicve methemoglobin. It can be caused by ingestion of certain drugs or compounds. A genetic form is due to nadh-cytochrome b5 reductase deficiency (an enzyme) which causes decreased oxygen carrying capacity of the blood, with resultant cyanosis (=blueness) and hypoxia (low oxygen in blood).