Journey of a Diamond

I was looking at this thing about the journey of a diamond on msnbc's website, and it is very interesting. It had a lot of black and white photographs of the miners in Africa and their lives, and it made me think about what Mark said the other day about how poor people are always photographed in black and white. I think black and white has a very different feel from color, and there should be an intention behind using it. When do you think it is appropriate/necessary to use black and white versus color to tell a story? What kind of effect do you think it has?