Green’s Dictionary of Slang

lavender adj.

(orig. US) a euph. for homosexual and anything referring to homosexuality; also as n., homosexuality.

[[UK] ‘The Ninety-Ninth Hussars’ in Songs for the Army 46: Sir Lavender Silk was a pretty young man, [...] / His men, though respectful, had thoughts of their own / Which might have spoke out if they chose, / That Sir Lavender Silk had the aspect alone / Of a Lady dressed up in men’s clothes!].
[US]M. West Pleasure Man (1997) Act I: stanley: And don’t you annoy the boys, Violet. paradise: Lavender, maybe, but violet never.
[US]W. Winchell On Broadway 21 Apr. [synd. col.] In the Waldorf Sert Room: ‘He eats raw hamburger once a week – sort of tempers off the lavender in him.’ [Ibid.] 18 Aug. When he goes across the street the traffic light turns lavender.
[US] in G. Legman Limerick (1953) 107: There was a young colonel from Trent / Who lived in a lavender tent.
[UK]I. Fleming Diamonds Are Forever (1958) 128: Coupla lavender boys. You know, pansies.
[US]Guild Dict. Homosexual Terms 27: lavender (adj.): A widespread term implying homosexuality. ‘To perfume with lavender ...’ Thus the ‘perfume set’ of a century ago applied lavender to mean homosexual, since the first males of the era past who used ‘perfume’ were considered feminine.
[US]A. Maupin Tales of the City (1984) 153: Chairman Jesus loves you! He loves all of us! The black and the brown and the yellow and the white . . . and the lavender! The last color was directed at the man in the prom gown.
[US]H. Max Gay (S)language.
[US](con. 1940s) Kennedy & Davies Boots of Leather (2014) 198: ‘“What the hell are you?” [...] “A lavender butch.” This meant she was butch, but femmy’.
[UK]Guardian Weekend 21 Aug. 5: There were several comments about beards and lavender friends.
[US]J. Ellroy ‘I’ve Got the Goods’ in Destination: Morgue! (2004) 170: We want Rock Hudson in Giant and Rock at the Lavender Lounge.
[US]J. Ellroy Widespread Panic 4: Confidential labeled him ‘the Lavender Lilliputian’ and ‘Princess Tiny Meat’. 23 Sept. 🌐 [headline] Rock Hudson Was Hollywood's Most Famous ‘Lavender’ Groom [...] Gates always insisted that it was a legitimate marriage, not a ‘lavender marriage,’ as unions arranged for gay stars were known.

In compounds

lavender boy (n.) (also lavender lad, ...lips)

a male homosexual; thus lavender-lipped adj.

[US]Monteleone Criminal Sl. (rev. edn).
[US]D.W. Cory Homosexual in America 112: Most of the words [in Amer. Dict. of Slang] were of infrequent usage: agfay, lavender boy, mason, nola, queervert.
[US]Trimble 5000 Adult Sex Words and Phrases.
[US]K. Brasselle Cannibals 105: How is it possible to escape Lavender Lips?
[US]B. Rodgers Queens’ Vernacular.
[US]Maledicta VI:1+2 (Summer/Winter) 132: Twilight men was common in the days of lavender lads and pansies.
[SA] in ‘Ben Trovato’ On the Run (2007) 32: Some lavender-lipped, bunny-hugging mooncalf went snivelling to the Constitutional Court.
lavender cowboy (n.)

an effeminate man; thus a male homosexual.

[US]Harold Hersey ‘Lavender Cowboy’ 🎵 He was only a lavender cowboy, / The hairs on his chest were two, / But he wished to follow the heroes / And fight like the he-men do.
(ref. to 1935) P. Stanfield Horse Opera: The [...] 1930s Singing Cowboy 119: In Tumbling Tumbleweeds the heavies call Autry a ‘lavender cowboy,’ an obvious insinuation of effeminacy and homosexuality.
‘Fashion Police’ Durango Tel. 22–28 Aug. 🌐 This is an excellent specimen of what we like to refer to as the ‘Lavender Cowboy.’ These individuals have embraced western ideals and a pioneer way of life, but usually lack the requisite callouses and fencing skills that are common to most actual cowboys. Large chunks of turquoise, brilliantly bright bolos, and lizard or ostrich skin Tony Lamas are all tell-tale signs of the ‘Lavender Cowboy’.
lavender desperado (n.)

(US gay, west.) a sexually eager gay cowboy.

(con. late 19C) J. Nevins ‘Western frontier gay slang’ on Twitter 2 Mar. 🌐 ‘lavender desperado’ = horny gay cowboy; presumably after ‘alfalfa desperado’ (a farmer).
lavender law (n.)

legal issues, practice and study pertaining to the gay and lesbian community.

[US] Queer Sl. in the Gay 90s 🌐 Lavender Law – Legal issues, practice and study pertaining to the gay and lesbian community.
lavender marriage (n.)

an ostensibly heterosexual marriage in which one or both partners is/are in fact homosexual or bisexual; typically entered into by celebrities.

J.C. Biddle-Cope Mad 6: This drab and lavender marriage carried her out of John’s reach, and relieved him of an agonising consciousness of responsibility towards her.

In phrases

have a dash of lavender (v.)

to be marginally homosexual.

[US]C. Porter ‘I’m a Gigolo’ 🎵 I should like you all to know, / I’m a famous gigolo. / And of lavender, my nature's got just a dash in it. / As I’m slightly undersexed, / You will always find me next / o some dowager who's wealthy rather than passionate.
[US]G. Legman ‘Lang. of Homosexuality’ Appendix VII in Henry Sex Variants.
[US]B. Rodgers Queens’ Vernacular.
P. Theroux Old Patagonian Express [ebook] My brothers were calm, one ironical, the other squinting at a trim young man on the platform and saying, ‘A dash of lavender, Paul – watch out, he's getting on!’.
[US] in L.R. Murphy Perverts by Official Order (1989) 54: ‘As they say in sets I have known,’ he confessed, ‘it is a dash of lavender.’.
T. Doherty Pre-Code Hollywood 121: The Hays office would not stand for ‘more than a dash of lavender’.
streak of lavender (n.)

an effeminate man.

[US]A.J. Pollock Und. Speaks n.p.: Streak of lavender, an effeminate man; a sissy.