When selecting images, think about whether the image works best in color or grayscale. Here are some guidelines to help you decide which will serve you best:
Grayscale photographs work best when the image exhibits strong textures. For example, wood grain, battered metal and repeated patterns work well. Grayscale photos appear to be and advantage when there's high tonal contrast. If an image lacks color saturation or color contrast, it might be best to run it in grayscale.
An image will work best in color when strong color contrast exists. Examples of colors that contrast well are blue and orange, light green and red or purple and yellow. A photo with strong color contrast does not always have strong tonal contrast, and thus may look better in color than in grayscale.
Some grayscale photos lack enough texture and contrast to make them visually appealing. In such cases, it is possible to colorize them to bring out more detail.