Ibn Abbas (ra) narrated that the Raya of the Messenger (saaw) was black and his Liwaa was white.
During the battle of Mu'atah the Messenger (saaw) was delivering a Khutbah in Medinah. The Messenger (saaw) was telling the Muslims about what was happening in the battlefield. He (saaw) informed them Zayd (ra) was killed and Ja'far took over the Raya (black flag) from him, then Ja'far (ra) himself was killed, so Abdullah Ibn Ruwahah (ra) took over the Raya (black flag).
Al-Barra'a Ibnu Azeb (ra) was asked about the Messenger's (saaw) Raya so he said: "It was black, had four corners and was made of wool." These and other ahadith clearly prove that Muhammad (saaw) had designated a flag for his Ummah.
The Messenger of Allah (saaw) conquered and entered Mecca with a Liwaa (white flag). Allahu Akbar!