This is a really nice technique to make photos look dynamic and interesting. It can be used very well for coloring small, subtle effects like a subjects eyes for example or for more dramatic effects.

Step 1

Open up the picture you want to work on in Photoshop. I used this image from www.sxc.hu:

Step 2

Now you will need to duplicate the background layer. Go to layer > duplicate layer or simply drag the background layer onto the create a new layer icon in the layers palette. Name your duplicated layer ‘mask’.

Step 3

Now we want to desaturate the mask layer to create our black and white image. Go to image > adjustments > desaturate. Now that we have our black and white image, we need to start adding color to the bits we want to show through. Go to layer > layer mask > reveal all. This will put a layer mask on our ‘mask’ layer. Make sure the layer mask is selected (it will have a white border around it). If not, just click on the thumbnail within the mask layer.

Step 4

Select a hard brush and with black as your foreground color, begin painting on the areas that you want color. If you make a mistake, select white as your foreground color and paint over your mistake. Take your time and zoom in to be as accurate as possible.

Eventually you will end up with your fully painted image:

There are quite a few ways to achieve this effect but using layers masks and brushes is the most accurate and effective.