Here is an account from *The Tablet* dated November 1, 1958 (p. 387) that corroborates what I previously reported from Father Jean-Marie Charles-Roux regarding the variations in the color of the smoke.
“Few people realize how easy it is to pick up Vatican Radio on the medium-wave band (196.2 m) with any standard radio in this country [England]. This was not the case before, but it has been a year since that changed, ever since the late Pope [Pius XII] inaugurated the new powerful transmitters at Santa Maria di Galeria. Last Sunday [October 26, 1958], nothing was easier than sitting in London and listening to the announcer [Father Pellegrino] express his enthusiasm about the color of the smoke. At five o’clock local time (six o’clock in Rome), he suddenly declared [at 6:02 p.m.]: “The smoke is white... there is absolutely no doubt. A Pope has been elected. Habemus Papam.” But then, the smoke seemed to turn black [at 6:05 p.m.], and he said that perhaps we should wait for confirmation of the news; then it clearly turned white again [after 6:05 p.m.], a loud cry of “Evviva il Papa” rose from the crowd in the Piazza, and the presenter cast caution to the wind: the white smoke, he said, was too dense and too steady [since 5:53 p.m.] to leave any room for doubt. Then caution got the better of him [since the last wisps of smoke were gray], and he declared that only when the lights came on in the Hall of Blessings could one be certain that a pope had been elected. But, he insisted, the slightly dark color of the white smoke could only be due to some technical problem: there was too much of it, too dense, for anyone to think otherwise. Yet the minutes ticked by and no lights appeared; it was 5:20 p.m. [6:25 p.m.] when the announcer really began to think that a mistake must have been made after all.
One of the most moving experiences of my life was listening on Vatican Radio to the Mass celebrated at midnight on October 8 by Archbishop Tardini, just a few meters from the bedside of the dying Pope [Pius XII]; every whisper, every word, the turning of the pages of the missal, and the rustling of the liturgical vestments were audible, as well as the emotion in the celebrant’s Latin and the responses of all the participants.”
This last detail proves that Vatican Radio could be easily received and that the news of the white smoke quickly reached the entire world.
Translated with DeepL.com (free version)
(Source: first comment)