It is the photographing of ordinary things, in extraordinary light, which results in extaordinary photographs...- David Young
Color TemperatureLighting is also categorized by temperature and measured on the Kelvin scale. Daylight, or neutral light, falls in the 5,000-6,000 degrees Kelvin range. The adjectives cool and warm, are standard when describing the temperature of color but they can be misleading. Warm lighting has yellow to orange tones as found outside in late afternoon and produced by incandescent bulbs. In the the below chart, however,warm lighting is on the low end of the Kelvin scale. Cool lighting has blue to green tones and is found on the top end of the Kelvin scale. Many knife photos taken in shadow or on cloudy days will show cool blue tones because of the higher temperature of that type of light.
This unmanipulated photo was taken just after the earlier posted direct and diffused lighting images.
The cool blue tones are produced by the higher temperature of the shadowed light caused by a dark cloud.Daylight balanced bulbs are engineered to be around 5500 degrees kelvin, the color temperature of sunlight. Standard flourescent and incandescent lights are less than 5500k, and before digital cameras, it was common to see these bulbs produce images with green and yellow tones.
More on Color Temperature: http://en.wikipedia.org/wiki/Color_temperature Many cameras have auto white balancing features and the color tone, or temperature, of your lighting can also be somewhat corrected in most photo editing software. Eighteen percent gray cards are usually gray on one side and white on the reverse to assist in white balancing. I will further discuss color balancing in a post about image editing software.
I learned to take photographs before the digital era and I used to spend countless hours in a dark room printing color photos for publication. The best looking photographs were always produced by controlling the temperature of the light when the photo was taken rather than trying to compensate or create for color tone in the dark room. You should search for and/or create bright, diffused and neutral to warm toned light before the photo is taken. Additionally, for the best results you should use only one type of light source rather than mixing, for example, flourescent with tungsten or daylight with incandescent.