From Longman Dictionary of Contemporary Englishiron-greyˌiron-ˈgrey British English, iron-gray American English adjective DCBiron-grey hair is dark grey
Examples from the Corpus
iron-grey• Her iron-grey coat was black with sweat and dust, her thin sides heaving, her eyes rolling.• His iron-grey hair and moustache were neatly trimmed.• She was elderly, short, and rather stout, with iron-grey hair closely cropped.• His iron-grey hair was parted in the middle and he had the mutton-chop whiskers of a bygone age.• There is a beautiful little iron-grey mare here that Alejandro has frightened out of her wits and says is too wet for polo. 