Green’s Dictionary of Slang

1. a person with light-coloured hair, a white blond; thus an old person with gray or white hair; thus cotton-headed.

1891		Dalles Dly Chron. (OR) 2 Apr. 4/3: He was a jolly fat chap, with [...] hair that gained him the title of ‘cottontop’ with all the children of the neghborhood.
1892		Eve. Star (Wash., DC) 22 Dec. 9/4: [headline] Cottonhead Sam Acquitted.
1897		Copper Co. Eve. News (Calument, MI) 17 Feb. 1/4: Schmidt, a wortghless young feloow, better known around the village as ‘Cottonhead’ on account of his extreme blond hair.
1900		E.H. Babbitt ‘College Words and Phrases’ in DN II:i 30: cotton-top, n. A white-haired man.
1900		Brownsville Dly Herald (TX) 25 Jan. 4/1: That ‘cotton-headed’ Southern warhorse and hero [...] Gen. Joe Wheeler.
1909		Richmond Cliax (KY) 23 June 5/2: ‘Cotton-top’ Wills, the latest additon to the Pioneer pitching staff.
1912		Washington Times (DC) 11 July 12/1: ‘Cottontop’ Turner failed to hit safely.
1921		DN V 160: Cotton-top, n. A white-haired man.
1930, 1935, 1960		in DARE.
1965		D. Pearce Cool Hand Luke (1967) 138: A man actually asked to get up. It was Cottontop. [...] We all watched [...] the white-headed pink-skinned albino.
2000		Eble Campus Sl. Spring 2: cotton top – old person with gray or white hair.

2. a Swede [stereotypically blond Swedes].

1907

N.Y. Athletic Club Monthly Mag XVI 16: So here’s a hand to ‘cotton top’ the loyal, lusty ‘Swede.’.