In 1936, McLuhan’s last undergraduate year at Cambridge, his friend there¹ and later unofficial adviser on his PhD thesis, Muriel Bradbrook (1909-1993), published The School of Night: A Study in the Literary Relationships of Ralegh.²  Influenced or not by Bradbrook’s study, which he certainly knew³, McLuhan adverted to blackout (and associated themes like obscurity and somnambulism) throughout his career and did so both positively and negatively. Negatively, black signaled an omission, a failure of perception, a gap in awareness. Positively, the gap strangely designated by such obscurity was, as McLuhan would insist over and over and over again, ‘where the action is’. So black covered something up which needed to be discovered  — and so functioned as a signpost and means to what required recovery.

1944
As excessive activity [has] starved the other needs of man and sharpened the spirit of gain and commercialism [such that] an unofficial blackout [has been] ordained over the spiritual and intellectual areas of man’s nature. (Dagwood’s America)

1953
THE ADS ARE A FORM OF MAGIC WHICH HAVE COME TO DOMINATE A NEW CIVILIZATION  Most people must by now have seen the original advertisement featuring a Clifton Webb sort of gentleman wearing a white shirt and having a black patch over one eye. This advertisement sold a million Hathaway shirts in a few weeks, but few ever found out why. The ad was a piece of abstract art, of unabashed symbolism… (The Age of Advertising)

As illustarted below, McLuhan reverted again and again to the Hathaway man.  Not seeing that it was remarkable (let alone what was remarkable about it) seemed to capture for him not-seeing in general. The Gutenberg galaxy formula illustrated by the ad was: seeing can be blind.⁴ As McLuhan noted in testimony before the US Congress: “Opposites are often very similar. They’re complementary. Affluence creates poverty, public creates privacy, white creates black, learning creates ignorance.⁵

1953
The spoken word instantly evokes not only some recently conceived idea but reverberates with the total history of its own experience with man. We may be oblivious of such overtones as of the spectrum of colour in a lump of coal. But the poet by exact rhythmic adjustment can flood our consciousness with this knowledge. (Culture Without Literacy, 1953)

1954
like symbolist art, [advertising] is created to produce an effect rather than to argue or discuss the merits of a product. The Baron Wrangel, the man in the Hathaway shirt — white shirt and black eye-patch: what did it mean? Out of the millions who bought Hathaway shirts, how many could say what the ad meant? It was a piece of magic: irrational, meaningless. But it had a definite effect. (Catholic Humanism and Modern Letters)

1956
The manuscript page with pictures, colors, and correlation between symbol and space, gave way to uniform type, the black-and-white page, read silently, alone. (The New Languages, [McLuhan and Carpenter])

Gutenbergian visual emphasis fixes black and white on the same horizontal level in strictly sequential order. This is how print looks and how print functions. “The print reader is subjected to a black and white flicker that is regular and even. Print presents arrested moments of [just this] mental posture [and no other]” (The Gutenberg Galaxy, 158). By contrast, the acoustic allows the black to cut through the white, and the white to cut through the black, vertically. Only so can there be something like figure and ground. And if no figure and ground, then no ground and only figure — and if only figure, ultimately no figure either.⁶

1959
because of its static aspect, the written word inspires the human mind with doubt. This is the habit of the eye. This is the habit of the eye inspecting writing: black-white … yes-no … maybe yes-maybe no. Scepticism is the very form of written culture. (Communications and the Word of God)

1962
“She comes! she comes! the sable Throne behold
Of Night Primaeval, and of Chaos old!
(…)
Nor public Flame, nor private, dares to shine;
Nor human Spark is left, nor Glimpse divine!
Lo! thy dread Empire, CHAOS! is restor’d;
Light dies before thy uncreating word:
Thy hand, great Anarch! lets the curtain fall;
And Universal Darkness buries All.”
This is the Night from which Joyce invites the Finnegans to wake. (The Gutenberg Galaxy, 263/298)

These are the concluding lines (before its final short section, or appendix, on ‘The Galaxy Reconfigured’) of The Gutenberg Galaxy.

1965
There is a subplot in the famous Hathaway shirt advertisement of the baron with the black patch on his eye. The main plot is simply Hathaway shirts. The subplot, the one that really includes the whole audience, is the black patch which bespeaks the world of aristocratic intrigue, hunts for hidden treasure, and many other mysterious dimensions, all expressed instantaneously by the black patch. The subplot world, the sub-environment, is really that which includes the audience, and it is the power to effect this kind of inclusion that is the mystery… (Address at Vision 65)

1968
Black Is Not A Color (Dew-Line #1)

1970
White is all colors at once, but black is not in the spectrum. It is a gap. (…) The spectrum gap that is black (…) is not a color but an interval (Culture is our Business, 220, 226)

1970
When the separated or specialized senses are heavily over­loaded, one tends to black out, to merge. (From Cliché to Archetype, 196)

1972
You cannot have a written tradition of white markets (…) without an oral tradition of black markets… (Take Today, 171)

1972
The idealists share with the experienced and practical men of their time the infirmity of substituting concepts for percepts. Both concentrate on a clash between past experience and future goals that black out the usual but hidden processes of the present. Both ignore the fact that dialogue as a process of creating the new came before, and goes beyond, the exchange of “equivalents” that merely reflect or repeat the old. (Take Today, 22)