From Halopedia, the Halo wiki
Lee R. Wilsons approach to the Halo 3 boards varied depending how they were going to be used. During the story writing process Lee did quick sketches for meetings. When Lee knew his in-engine cinematic lighting role for the game, he began to work out the lighting plan within the boards also, beginning with grey tone on scanned sketchs, then moving on to fill color.
These boards were done for the Halo 3 announcement trailer.