Learn English – the etymology of “business” and “busyness”

The Oxford English Dictionary doesn't have doublespeak as a separate entry; I can only make an educated guess. The word double-talk already existed in 1938, according to the OED, and was originally American. But apparently it meant simply "deliberate gibberish" then, i.e. not merely ambiguous language, but nonsense talk that listeners were supposed to know meant nothing, uttered to comical or artistic effect.

1938 New York Panorama (Amer. Guide Ser.) vi. 156 Of late a humorously conceived system of language corruption called double talk ... has made itself felt. Ibid. 157 Double talk is created by mixing plausible-sounding gibberish into ordinary conversation, the speaker keeping a straight face or dead pan and enunciating casually or off the cuff.

1941 Time 16 June 61/1 Thirteen recorded versions of this pandemic double-talk ballad are available.

1945 H. I. Phillips Private Purkey's Private Peace xxii. 129 We got the right slant on bullies, greaseballs, double talkers, supermen, and dopes.

1948 Auden Age of Anxiety vi. 125 And all species of space respond in our own Contradictory dialect, the double talk Of ambiguous bodies.

After Orwell's famous novel 1984, published in 1948/1949, double-talk apparently acquired the (additional?) meaning "deceiving language", i.e. language that is deliberately ambiguous, or language that appears to mean one thing but in fact means another.

1950 Amer. Speech XXV. 190 Back in Tsarist times Lenin and his associates inaugurated this double-talk and double-writing—especially the latter—in order to deceive the Tsarist censors and police.

1952 C. Day Lewis tr. Virgil's Aeneid ix. 203 You'll find no Atridae here, no double-talking Ulysses.

This is probably based on Orwell's newspeak and doublethink. His novel was (partly) a critique of the practice and propaganda of the totalitarian regimes of his time, Fascist Germany and Stalinist Russia.

Newspeak is new language invented by politicians as propaganda, in order to influence people's thinking by changing their language (one of the principal mechanisms studied by Postmodernist philosophers and sociologists). The word is invented by politicians in the novel and is an instance of itself. By drastically reducing vocabulary, and making new, simpler words from the remainder, they hoped to control the people more effectively. Many modern euphemisms could be called, and are often called, newspeak, like "differently abled" and "Secretary of Defence".

1949 ‘G. Orwell’ Nineteen Eighty-Four i. 51 Syme was a philologist, a specialist in Newspeak. Indeed, he was one of the enormous team of experts now engaged in compiling the Eleventh Edition of the Newspeak Dictionary. Ibid. ii. 133 Do you know the Newspeak word goodthinkful? Ibid. App. 299 Newspeak was the official language of Oceania and had been devised to meet the ideological needs of Ingsoc, or English Socialism. In the year 1984 there was not as yet anyone who used Newspeak as his sole means of communication, either in speech or writing.

Doublethink is somewhat related to what modern psychology calls cognitive dissonance: first accepting one fact as true, then another, contradictory fact—without critical self-assessment, which would ordinarily result in elimination of one fact or the other. Orwell's politicians try to effect doublethink by means of using and propagating ambiguous language.

1949 ‘G. Orwell’ Nineteen Eighty-Four i. iii. 37 His mind slid away into the labyrinthine world of doublethink. To know and not to know, to be conscious of complete truthfulness while telling carefully constructed lies, to hold simultaneously two opinions which cancelled out, knowing them to be contradictory and believing in both of them, to use logic against logic, to repudiate morality while laying claim to it, to believe that democracy was impossible and that the Party was the guardian of democracy.

Considering the change in meaning of double-talk soon after the publication of Orwell's novel, and the emergence of doublespeak to mean the same a few years later, your sources (reasonably) assume that the word was deliberately coined as a (semi-)portmanteau of Orwell's newspeak and doublethink. The OED has 1957 as its earliest quotation:

1957 ‘M. Buttle’ Sweeniad ii. 55 In the literary weeklies, the languages of criticism and theology have become one and book reviews all sound like sermons written in the most holy ‘*Double-Speak’.

1961 W. Kaufmann in G. E. Myers Self, Relig. & Metaphysics 99 The theologians have a way of redefining terms in rather odd ways, and frequently engage in something best called double-speak: their utterances are designed to communicate contradictory views to different listeners and readers.

The asterisk and quotation marks in the first quote might indicate that the word was then quite new and explained in a footnote.

I found an interesting grammarian blog on this very topic. Essentially, the post avers that puce is dark purple, but acknowledges the false notion of a "puce green" still persists. (It's theorized that the term might be an adaptation of puke green, but also readily acknowledged that there's no strong evidence to prove that notion.)

Also, I found a dress on Ebay today that was described thusly:

This fabulous Chetta B size 14 cocktail dress is created in a gorgeous deep, rich eggplant purple with a shadow of puce green in a beautiful brocade that is 100% silk.

I suppose that would mean the dress in question is puce-on-puce?

Lastly, I typed "Puce dress" into Google's search engine, and then clicked Shopping; this is what showed up on my screen:

The conspicuously un-puce dress in the middle is being sold as used, so it might disappear from the search query results in a few days. However, it does present some tangible evidence that some people indeed mistakenly refer to pea soup green as puce green.

As for why such misperceptions persist and become widespread, it only takes one exposure to misinformation to lock it into one's brain. This reminds me of a friend who once related how, while working on a project in his garage, he playfully asked his daughter to fetch him a "sawdonkey", making what he assumed was an obviously humorous pun on the word "sawhorse". Problem was, his young daughter didn't know what that object was called, so she simply noted the reference, and tucked it into her brain. Several years later, she was working on a stage crew in college, and it took five or six people to convince her that the object in question was indeed called a sawhorse, not a sawdonkey – she even called her dad that night to verify.