This is the first photo I’ve attempted to mix black and white with colour:

I’ve taken a couple of bites at it, most recently with a tablet [as in the input peripheral] which I’ve borrowed from someone from work. It’s probably not a bad shot to try to apply the technique to in terms of subject matter. It’s just that it betrays the shallow depth of field towards the top of the image. The original shot was at F4, 47mm on my 28-235mm zoom, and shot at ISO 200. I’ve used a couple of layers: the first is an adjustment layer -> Hues/Saturation, which I’ve reduced the saturation to -100. I’ve then created a second levels layer, and used that to increase the contrast a bit. Then back in the saturation layer, I’ve painted the colour back in.