From Longman Dictionary of Contemporary Englishroyal blueˌroyal ˈblue noun [uncountable] CCa bright deep blue colour —royal blue adjective
Examples from the Corpus
royal blue• They had selected a full-skirted velvet frock in a deep royal blue which set off her auburn hair.• A box of royal blue was opened by the Court Chamberlain and the awards placed over the recipients' shoulders. 