Did the Messenger of Allah, may Allah bless him and grant him peace, anoint his hair and body with olive oil, or only his hair? And was the whiteness of his body due to olive oil, or was he originally fair-skinned?

The Messenger, peace and blessings be upon him, used to oil his head. It is narrated in Sahih Muslim from Jabir ibn Samurah that when he oiled his head, his grey hairs would not show, but when he did not oil it, they would appear.

As for oiling his body with oil, there is no explicit text about that. The report that states "as if his garment was a garment of an oil seller" has been weakened by some scholars, and interpreted to mean the head covering he wore.

As for the color of the Messenger, peace and blessings be upon him, he was fair with a reddish tint, not pure white. This is how scholars like Ibn Hajar al-Haytami and Ibn Qunfudh described him.