First make a duplicate of the image on a new layer, from the Layer menu select Duplicate Layer.
Now we will create an Adjustment Layer to alter the colours in the image. Choose New Adjustment Layer from the Layers Menu and select Hue/Saturation.
Click on the Colorize check box, Slide the Hue to -150 and set the Saturation to -50 (if you want a B&W image don't select Colorize, and set Saturation to zero, this is one way of creating a monochrome image). This is after the the Hue/Saturation changes.
Now we you want to restore something to it's normal coloring.
Click on the layer mask on the Hue/Saturation layer in the layers palette, the layer mask is the white box to the right-hand side, it will have a double border around it once it is selected.
The layer mask controls which parts of the image are affected by the adjustment layer, any point on the mask with white pixels is affected by the adjustment, any area with black pixels is unchanged (grey pixels vary the strength between the two extremes).
You will see that the layer mask is initially all white, we want to paint in black to reveal unchanged areas underneath.
Select a suitable brush and select black as the foreground colour.
Now start painting on the Hue/Saturation layer mask.
If you're not too accurate with your painting just select white as the foreground colour and paint on the affected area to erase the error. And now the final image in all its weirdness.
The final product should look somewhat like this.
Notice that I didn't b&w however. That's just an option.
