The subdued color was an attempt to lend the boards a more "documentary" feel. That was what the art director requested at the last minute, after the boards had been drawn and colored. Decreasing the saturation seemed the only option short of a total redraw. Fortunately, it achieved the effect they were looking for.
There are some collage elements in these boards. It's not always worthwhile to draw every element when time is of the essence. What might be considered "cheating" in another context is just a means of enhancing verisimilitude and saving precious minutes where storyboards are concerned.