Hand coloring opens up an entirely new dimension in image making for the photographer.
Coloring can bring new life to old black and white images; one that reflects reality or creates a new, invented one. I've used Marshall's Oils to transform old black and white images from the Fremont Summer Solstice Parade, which I photograph every year, into full-color scenes that match the vibrancy of the event, and which I now shoot in color.
Selective coloring can be used to highlight certain areas of an image, creating a surreal scene that focuses attention on whatever the photographer chooses.
Or it can be part of the previsualization when photographing a new scene: "Hmm, I love everything about this scene except that those trees are just so green, and that sky is always blue, blue, blue..." Choose to alter the natural color scheme, or make a sunny day out of a gray one.
The process of painting color onto a photograph is wonderfully immediate. It gives the artist control over what is created in the moment, which can be a welcome respite from the many technical steps usually required between shooting and enjoying the final print. As photographers, we lose access to this immediacy; hand-coloring provides a bridge, and a fun way to get our hands dirty.
I love any technique in photography that breaks the bounds of the traditional rectangular, sharply focused, accurate representation of the world. One way I do this is by my use of a fuzzy image frame around my Holga images. This creates a unique look, and focuses the viewer's attention in a completely different way than does an image that uses the traditional format.
Hand coloring is another great tool that allows the artist's vision to flourish in an individual way.