I know the very thought of unscientific results being reported in this newsgroup drives some bonkers - tough tookies.
My very unscientific experiment with red mulch (compared to many, many, many years of growing tomatoes around here) has been a rousing success. I have virtually no blight. I have tons of tomatoes. Why the hell did I plant 15 plants? Hehehe. Seriously, the red mulch seems to work. I have no idea if black would do as well, it wasn't on sale :o)