How do I do this?

[Sheiky]

Argg Bob you were faster than me [:P]

But not so much as to eliminate all color

what do you mean? If you put your vibrance or saturation to -100 for example, there won't be a lot of color left. You can do this for individual colors as well so you can have only 1 color in your shots in the end. It's a bit like the Sepia effect I think.