I did some research in this regard, and below are my findings. There were many flags used in Brazil during colonial times; there were the flags of the navigators who traveled to those lands, the Portuguese royal flags, and others. The most representative one is, I think, is the flag of the Principality of Brazil (Brazil was formally elevated to a Principality in 1645 by the Portuguese king João IV). This is the flag: However, this flag wouldn't be consistent with the colors of Portugal (which might be important in regards for players to quickly identify flags and respective unit colors?). But there were two other flags of the colonial period in Brazil which would. They are, respectively, the merchant marine flag of the Portuguese Empire: ...and the personal flag of the Pedro II of Portugal: Considering the concerns of consistence with Portuguese colors, I personally lean towards to Portuguese merchant marine flag, because: A) It makes sense to use a merchant marine flag as the flag of a colony, B) The personal flag of a Portuguese king is too representative of the mainland itself, compared to a merchant marine flag, which is by its own nature a representation of the motherland's actions in overseas lands. But, if consistency between flag and player colors aren't an important concern, then I think the flag of the Principality of Brazil is the best one to use... because it is the most representative one of Portuguese America during colonial times. Another possibility is using the coat of arms of colonial Brazil: It has the advantages of being both representative of Portuguese America, and having the Portuguese colors (since the tree is green). My source for research in respect to this matter was: Milton Luz, A História dos Símbolos Nacionais, 2005, pp. 54-59 and 102-110.