The assumption is that the prints are B&W since it is a B&W competition. One uses a color filter to get a colored object more notice in an image. Once one adds an actual color to a B&W print, the print is no longer B&W. It is a colored print that is mainly B&W. B&W is just B&W, no color.

Because B&W is just B&W, I made the assumption that the OP was wanting to make an object more black or white by using a color filter of some sort to emphasize the object. There seemed no logic to add actual color in a B&W competition.