Green’s Dictionary of Slang

1. of a black person, light-skinned.

1896		Irving Jones ‘Honey, You’ve Got to Leave’ 🎵 There’s a lemon colored lady, the coons call flat-foot Sadie.
1907		Thomas S. Allen ‘Let Me Be Your Lemon Coon’ 🎵 Ebenezer Johnson was a yaller coon.
1928		C. McKay Home to Harlem 58: A lemon-colored or paper-brown pool-room youngster.
1960		P. Oliver Blues Fell this Morning 80: To differentiate between their many shades of colour [...] ‘brightskin,’ ‘high yaller’, ‘lemon’.

2. (US) useless, second-rate.

1906		T.A. Dorgan in Zwilling TAD Lex. (1993) 54: Lemon idea.
1924		G. Henderson Keys to Crookdom 410: Lemon. Something worthless.