"the press," by 1824, and especially from 1831, British English. For the other three, see estate. Earlier the term had been applied in various senses that did not stick, including "the mob" (1752), "the lawyers" (1825). The extension to the press is perhaps an outgrowth of the former.
Hence, through the light of letters and the liberty of the press, public opinion has risen to the rank of a fourth estate in our constitution; in times of quiet and order, silent and still, but in the collisions of the different branches of our government, deciding as an umpire with unbounded authority. ["Memoir of James Currie, M.D.," 1831]
[Newspapers] began to assume some degree of political importance, during the civil wars of the seventeenth century, in England; but it is not until within the last fifty years that they have become, — as they are now justly styled, — a Fourth Estate, exercising a more powerful influence on the public affairs of the countries in which they are permitted to circulate freely, than the other three put together. [Alexander H. Everett, "Address to the Phi Beta Kappa Society of Bowdoin College," 1834]
also colour-blindness, "incapacity for perceiving certain colors due to an absence or weakness of the sensation upon which the power of distinguishing them depends," 1844, the native word, used in England instead of French daltonisme (by 1828), after English chemist John Dalton (1766-1844), who published a description of it in 1794. From color (n.) + blindness.
The continental philosophers have named it Daltonism, a name which has been strongly objected to by almost every English writer who has discussed the subject, on the ground of the inexpediency and undesirableness of immortalizing the imperfections or personal peculiarities of celebrated men by title of this kind. ... The name "Color-Blindness," proposed by Sir D. Brewster, seems in every respect unexceptionable. [Littell's Living Age, vol. v, April 1845]
Noted as inexact (very few people who can see are blind to all color), "the term is applied with much laxity to any constitutional inability to discriminate between colours" [OED]. In figurative use, with reference to race or ethnicity, it is attested from 1866, American English. Related: color-blind (adj.), which is attested from 1854.