I don't know what connections are available on a bose system, but if you are using component video (3 cables, red, blue, green) you can get a green picture, if you are using s-video and something has gone wrong with some of the pins or the connector is not tightly seated it is possible to get a black and white picture.
I will gues you have checked, and your TV is showing regular TV channels with color, or a vcr, which will tell us that it's probably not the settings on the TV.
Does anybody know why our bose lifestyle 35 would suddenly start playing dvd's in black and white? As far as we know none of the settings have been changed and all of the appropriate cables seem to be plugged in correctly. Can't get ahold of bose until tomorrow - just wondered if someone knew how we could fix this.