Fernando Poo is a former Castillean colony (equivalent to the island portion of Equatorial Guinea *here*.) It was granted independence on 12 October 1968. The island adopted its national and maritime flags on 1 November of that year.
Note: a possible conflict in QSS here -- the article Iberian Peninsula says: "Castile and Aragon also hold the Canary Islands and Fernando Po in condominium."
Note: as early as June 2004, Fernandoo Poo is described as a "former Castilian colony".