digital camera lenses consist of both cooling and warming filters. Both are used to change the white balance. For those who do not know, white balance is a process to remove unrealistic color casts. Ever notice a blue tinge on compact camera photographs? That's because the white balance is off. Besides correcting color cast, the filters can also be used to add unrealistic color –which is more the case nowadays.
Thanks to automatic white balance adjustment and photo editing programs, the filters aren't often used to correct a photo. Certain situations, though, may call for their use such as unusual lighting or underwater photography. White balance cannot restore color when there is a large amount of monochromatic light and if it does, you can expect a big amount of image noise.
A colored filter will either lighten or darker opposite colors. For example, a red filter will darken green and blue. You can even use colored filters when taking black and white photography. Many colors look very similar when converted into grayscale. This will leave you with flat photographs that lack any contrast. A color filter will let in its own color of light and block out the rest. The result will be colors matching the filter will appear brighter while the other colors will appear darker. Obviously in black and white photography that means lighter or darker shades of gray –making images more dramatic.