"'white' person, person of European descent," by 1830 (of a white horse by 1828), from white (adj.) + -y (2) and -y (3). Earlier as an adjective, and Whitey-brown was a 19c. descriptive color name, used to describe, among other things, mulatto skin.
Blackey will overreach if he finds an opportunity; but the probability is, that his rogueries are often but apt imitations of Mr. Whitey, who would fain always be thought to be a pattern of honesty. [Capt. Hugh Crow, "Memoirs," London, 1830]
Negro troops doing provost duty in Norfolk; keeping the white people in order. On a visit to Norfolk one can see white Southerners, arrested for sundry misdemeanors, working on the public streets, under negro guards. ... It is quite a change to see, in Norfolk, negroes forcing white men to work, at the point of the bayonet; calling out to them: "No loaf'n dar!" "Move quicker, Sah!" "Hurry up dar, Old Whitey!" and similar orders. Tables turned! [diary of Lieut. S. Millett Thompson, 13th New Hampshire Volunteer regiment, U.S. Army, Jan. 25, 1864; diary published 1888 by Houghton, Mifflin & Co.]