When the time comes to work out which scheme is better for the overall composition and story, there are two primary deciding factors which will help you. In respect of which scheme you chose, always shoot in colour with your camera set to RAW, that way you have maximum image flexibility when it comes to post production (the beauty of RAW).
So when you arrive at the cross road, ask yourself,
- Does my image rely on shapes, patterns or tones? - Best suited to B&W
- Does my image rely on colour interaction (complimentary colours) and vibrancy? Best suited to colour
Keep in mind, the two categories are not mutually exclusive, there will always be times where you could tumble into either bucket. But because digital allows for free experimentation, punish those pixels and see what happens.
Example 1 - The Cyclist
Black and white was chosen for this image because of the uneven colours present. Although it is a little difficult to see now, in the original colour version of this image the trees were different shades of brown and the dry/wet sand mixed in with the fallen pine needles were distracting. By performing the black and white conversion the resulting image is much more compelling and the focus is drawn to the subject matter, the young competing cyclist.
Example 2 - Koru
The black and white conversion in this image helps draw in the viewer to the shape, texture and the spiky arrangement of the hairs on the plant. In colour, the image suffers from a harsh green background from the surrounding foliage. Not only does the conversion focus your attention on the plant, it also provides an almost studio quality backdrop with very subtle variations in grey shades, replacing what was a ghastly nuisance.
Example 3 - Mushroom
The mushroom in this image stands out because it is orange. If it was not for its vibrant colour, we would have walked right past it while hiking and missed the shot. For this reason, the final product remains in colour and is the perfect example to illustrate how your eye is drawn towards the point of difference in an image. The mushroom being hard to miss, is obviously the point of difference, playing on the striking balance between the green moss, blue dew and the poison red of the fungus; in black & white the magic of the image would be lost.
Example 4 - Guitarist
The blue from the shirt, orange guitar and the flare coming from the right are all colours which compliment one another. Complimentary colours are easily identified on a colour wheel. These are colours which work in harmony with one another and are pleasing to look at without being distracting. If there were too many clashing colours in the scene, a black and white conversion would have been advantageous.
As demonstrated, there are times where black & white just works better for the overall image. But it is a creative choice on which the artist decides before publishing or printing their work. Often there is no right or wrong and it becomes subjective. So always ask yourself questions while editing and making exposures. This will help guide the creative process, build your unique photographic style and ultimately only improve your work.