Selective Black and White

One of the techniques that I've learned to use and enjoy is selective black and white photography.  Sometimes there is a part of the image that I really want to have the viewer focus on, and the depth of field that's in focus isn't enough to do it.  If the background is too cluttered, it distracts from what I consider the main reason for the image.  I have to use Photoshop or Lightroom to do this selective black and white effect.  At first I only understood how to do this with an entire color spectrum;  In the picture of lavender, all the stems and leaves were green and the photo was too vivid/intense with that much green and purple, but I wanted to keep the nice purple from the flowers.  I figured out where I could select a specific color (green) and turn its saturation completely off, meaning anything that had been green became grey.  It worked easily enough in that photo, but there were other instances were the main focus of the photo had matching colors to something else in the photo (like the yellow double line and yellow cars, or the yellow stems of the yellow orchid), so I couldn't just turn the saturation of that specific color off.  I had to figure out how to selectively do it, and that's where I learned about the "burn" tool.  Basically, you can set the tool to do specific details over whatever part of the photo that you drag the burn tool across.  it's actually a technique that was once used (and still used) in darkrooms with film, where they could "burn" parts of the developing film by adjusting how much light hit certain parts of the film during the developing stage, thus changing the end resulting exposure of the photo.  In my digital darkroom, I figured out that I could "burn" out all the colors of my photos by dragging this tool across only the sections I wanted to turn into black and white, and suddenly I could be a whole lot more precise with the technique.