Chicho Ibañez Serrador wanted to shoot this show in color using film, but TVE forced him to shoot it in black & white, since Spanish TV at that time could only be broadcast in that format The PAL color PAL system arrived to Spain two years later in 1969, and it wasn't used regularly until December 1972, and there was no budget to shoot it in color anyway.
Augusto Algueró didn't send the musical score in time to film the musical numbers, so they had to be filmed without music and add it in post-production.
Spanish Television censor man was heavily against the making of this show and threatened to resign if it was greenlit. Later on, after the show had won a prestigious prize given by the Vatican, Chicho Ibáñez Serrador saw him, he teased him saying "What do you have to say? A prize given by the Vatican, what do you think?" to which the censor man just said disdainly "Suit themselves".
The dictator Ultra Catholic government never had the intention of broadcasting the show in Spain, they just wanted it to travel outside to win prizes and give a fake image of Spain being an open, progressive state. However rules of the Montreux festival demanded the show to have been released in its country of origin, on the participant's main national TV channel, to win its award, the prestigious Rose d'Or. What they did was wait one day for the end of the scheduled broadcast around midnight, wait for half an hour of the transmission switched off in a test-card and then reopen the transmitters by surprise, when most people had already turned off their TV's and gone to bed, and broadcast the show, all of this without further announcement anywhere that the show was going to be broadcast. As such very few people actually watched on its initial release.