This was the first major studio production to be photographed entirely in 2-color Technicolor. Zane Grey had stipulated in his contract that the film was to be made in color in order to get maximum effect from the setting.
Although contemporary reviews consistently list the film's length @ 5775 feet, Technicolor's internal records document it as having only 3854 feet of Technicolor footage. So it's quite possible that about 1920 feet of the completed feature consisted of tinted black and white footage, which, out of necessity, was used to simulate colors not achievable by the Technicolor palette, such as blue, for example, and/or for night scenes which were not photographed with the intense amount of lighting required by the Technicolor cameras. But, as far as publicity was concerned, it was still a "100% Technicolor Feature."