Yet, sometimes it is appropriate.  The example commonly used  is to draw attention to something, such as a rose in a bride’s hand.  This has been done so many times, it has become cliche – almost everyone has one.  As a result, I tend to avoid this technique like the plague.

However, it is occasionally appropriate for a given photo.  For example, a photo that is already essentially a monochrome, despite being in color.

A closed jogging trail, essentially a monochrome

The photo to the right is just such a case: despite being in full color, it was an overcast day.  Surroundings were almost entirely green, except for the odd wildflower and the orange sign.  As such, it’s effectively a monochrome, but a green version.

This photo was taken with the intent of showing the incongruity of the construction.  You have a naturally-worn trail with wildflowers and grasses growing as they might, and both the grass and the trail lead to a single conclusion: as sign saying “you shall not pass.”  The composition leads the eye there, but the orange warning colors of the sign are lost among the sea of bright, vivid green.

To draw attention to the sign, there are a variety of techniques that can be done.  We could drop saturation a bit on the greens, making the orange stand out.  We could brighten the oranges, to make them stand out.  We could HDR it, or use luminosity (dodging & burning) to attract attention where it needs to go.

All of these techniques leave something to be desired.  Reduced saturation will still leave colors competing with each other. Enhancing the oranges or using HDR techniques will turn the image radioactive.  Dodging & burning will have a good chance at getting the desired result, but requires subtlety, something that (I believe) would be lost on most.

Selective color in this one instance is the best way to bring attention to the sign. Witness (mouse over to see full color version):

Trail closed, selective color