1840 R. Browning Sordello ii, in (1896) I. 128/2 Whose shape divine, Quivered i'the farthest rainbow-vapour.
1930 24 Nov. 17/1 The Superoptimists live in a land of steam heat, rainbow vapors, lingering perfumes, [etc.].
2003 (Nexis) 3 Oct. (The Edge section) e28 These rainbow vapors, however, represent ‘Minuteman Missile Being Tested Over the Skies of Los Angeles’.