The earliest softcore artist reference images came overwhelmingly from Paris, and they did indeed tend to be white. As a result, black women tended to be viewed from the beginning as French culture has always had a very complicated relationship with black bodies--see for example the case of Bartmann, the Hottentot Venus, who was overwhelmingly eroticized but also compared to an animal and who appealed to a sense of colonial superiority.

As a result, black women became an especial rarity in early pornographic images and videos. Indeed, in the biggest archives of erotic images to survive, the Uwe Schied and the Kinsey, the images of black women are limited to mere handfuls. I would be interested in knowing what archive you are using, OP. This rarity was exported to England and then America, to the effect that today it is far more common for pornographic actresses to be white (and better paid) than to be black.

On the flip side of the coin, black men were often eroticized in the opposite way, as a fetish or cuckold object, especially when they were paired with white women--in America there was an element of danger (and often racism) that fed off of southern fears and resentment of the black bogeyman who would steal their blond white wives.

There was not really many pornographic videos that became popular in the 1960s, but there is, however, the blockbuster Behind the Green Door that appeared in 1973 and kicked off the golden age of pornography in the 70s and 80s. The film [DEFINITE NSFW LINK TO ACTUAL PORN] features a blonde hair, blue-eyed Marilyn Chambers who plays a wealthy San Fran socialite who is abducted to a sex club and in her words "loved as she's never been loved before."

She engages in lesbian sex (which was also rather remarkable for the time) and then the main 'climax' scene of the film is this profoundly bizzare and amazing 45 minute sex scene with black actor Johnnie Keys to smooth jazz until she has an orgasm...then then it gets weirder where there's this whole trapaeze scene and a final closing scene of semen flying through the air for 7 minutes.

Anyhow, the actors in the film were very aware of the groundbreaking material they had. In The Other Hollywood: The Uncensored Oral History of the Porn Film Industry they recount their experiences:

MARILYN CHAMBERS: I was still pretty nervous. The black-and-white sex thing—I knew this was a very big taboo, as it still is in our country. And I thought, “Now my father’s really going to kill me!” Ha, ha, ha!

JOHNNY KEYES: I was fucking the hell out of this chick—I was acting like I was ten thousand Africans making up for that slavery shit. Here’s this white woman that the African is fucking to get revenge on all those white motherfuckers that used to rape our mothers and aunts all those years ago, right? That’s what I used as an incentive to fuck Marilyn Chambers.

MARILYN CHAMBERS: That scene broke out of the old porno mold of handheld cameras and lousy color and showed people that there’s a great deal of beauty in the mystery and majesty of an orgasm. I call it artsy-fartsy now because I’ve seen it so many times, but the first time a person views it, they’re kind of stunned. And they get all horny inside. Of course, that sequence is the ultimate in the fantasy of man conquering woman.

Marilyn had forgotten to note one thing to the director before they started--she had some some modeling for a soap company. Ivory. Yes she was the Ivory Soap model and was on the new box EVERYWHERE in the country. The director knew he had money on his hands.

ARTIE MITCHELL: Straight fluke! What an avalanche of free publicity! We were just standing in the wings. It came up, and we just had to play the cards that were dealt out. You can’t break the chariot of Procter & Gamble’s Ivory Snow—which is sixty percent of their action—that often, you know? The girl who was on the Ivory Snow box before Marilyn was on it for twelve years. They don’t fuck with that box! That box is their baby. They went through two years of backroom bullshit to finally agree that that was the look they were going for—the young, blond mother image. Only this young blond turned out to be a porn star. And then we went to Cannes right as the story was breaking.

MARILYN CHAMBERS: Never before had an adult film been reviewed at the Cannes Film Festival. It was quite something...The press was just phenomenal. I mean, I was just inundated. I was famous overnight because of the Ivory Snow box and Behind the Green Door. Kind of a paradox, but the press ran with it. Show magazine was saying, “This is the new Marilyn Monroe!” I got a ten-page spread in Playboy—a celebrity layout. I was signing thousands of pictures. And I started getting calls for straight movies.

The appearance of black actors and actresses in erotic and then pornographic material was complicated. They had to navigate all sorts of issues such as racism, sexism and colonialism. Black men could often do this by appearing or acting more animalistic or primitive (the stereotype about black men having larger penises comes from this). For black women, however, the bar was even higher and even to today there is a significant pay gap between white and black actresses in pornographic film.