Selective black and white in photography can be a great tool to direct the viewer to a specific place within a photo. By removing the color from all but your main target it becomes clear what in the photo you want to show.
Using Photoshop there is a very quick way of achieving this effect on some photos. Even though it work on lots of different subjects it goes extra well on macro shots where background is blown out, often in a short range on color.
To show off this effect I will be using a macro shot of a flower from my garden. The flower is colourful in pink against the green background.
There is good contrast in the photo from start which will also help us in using this technique.
By default the adjustment is selected and the layer mask is completely white so changes done will affect the entire photo.
Using the handle button you can instead of changing individual color channels just click and drag inside the photo to add or reduce saturation of that selective colourspace.
Since the flower is in a completely different color then the background I do not need to cut out or lasso any parts of it.
The result is a quick and easy selective color photo of the flower.