Could they be doing this in black and white due to the amount of blood and or gore that will soon be shown?
I ask this because didn't Tarantino have the same issue in Kill Bill Vol 1 where The Bride is Killing the Crazy 88's in the bar? The MPAA said they had to tone down the blood so He changed the color to Black and White.....wait I found it..
Black and white (as well as black and red), were used to conceal the shedding of blood from television censors. Originally, no black and white photographic effects were going to be used (and in the Japanese version none are), but the MPAA demanded measures be taken to tone the scene down.