Thanks to Cook's Thesaurus, I have an answer to that question!
masa harina: This is flour made from hominy, and it's used to make corn tortillas and tamales. Look for it in large supermarkets or Hispanic markets. It's made with either yellow or white corn; harinilla is made with blue corn. Substitutes: masa (This is masa harina that's been reconstituted with water.) OR harinilla (blue, not yellow)