Looks like it will be "Tintin in the Land of the Soviets", which https://en.wikipedia.org/wiki/Tintin_in_the_Land_of_the_Sovi... says "is the first volume of The Adventures of Tintin" and "it was the only completed Tintin story that Hergé did not reproduce in colour" due to Hegré's "embarrassment at the crudeness of the work."