Hand-coloring has been used by photographers for over a century to add color to black and white photographs. This was done by hand painting the photograph with oil or watercolor paints. Unlike toning, which applies the same color to the entire image, selective coloring applies one or more colors to specific parts of the image.
The usual way to apply selective color is to use a mask and a solid color layer to apply color to specific parts of the image. However, by using Color Range selection and curves, you can achieve a more subtle look.