The color was not named for Royal Manchado. That was what the color was called in Argentina. The stallion was named for his color, not the other way around.
This color is relatively new to English speakers. Certainly there were Arabian people who were familiar with Trabag from the Wentworth book where she is pictured, but she remained singular as far as anyone knew until a little more than a decade ago. At that time, someone had inquired about "leopard patterned" Hackney on a mailing list for that breed. A friend of mine raised Hackneys, and passed the photo to me. The mare was not an appaloosa at all (though someone not familiar with patterned horses might mistake her for one), but that same strange pattern as Trabag. From there I was put in touch with her breeder. He put me in touch with a man who had published a small book called "Overos Manchado", detailing the cases of this odd pattern in a variety of pure breeds. The author noted that the pattern was found in others, but he did not detail those for fear of having the pattern associated with "impure" blood. (And he was correct - the other examples I have found over the years since have been unregistered Criollos and Polo Ponies.)
I had that book for years, but it was in Portuguese so it was quite a while before I got it translated. I did have the pictures, though - probably the largest collection of examples of the pattern. I mentioned that there was this new pattern to Dr. Sponenberg when we gave a seminar in Kentucky, and his initial response was "the sabinos down there are pretty odd". I assured him these were NOT sabinos. The points of origin for the white are all wrong for that. When he saw the images in the book I had, he agreed it really was something different. He was also able to get the book translated, which was a huge help.
In the period before Sponenberg's latest book was published - which was a few years before mine - we both tried in vain to track down the people connected with the book I had. I tried again before I went to press, since I would have loved to have gotten permission to run some of the photos from it. I had no luck either, so I reproduced the patterns verbatim using illustrations.
So that is the history of the term, at least here in the United States.