What’s the Difference? is a series of lighting tutorials. Each article responds to a single question. In this post, Jared Platt shows how to achieve different effects with CTO and CTB gels.
Color of light is a critical part of photographic lighting, but most photographers do not pay much attention to it when using flash. Each light source has a particular color cast to it, which is why your camera has white balance settings. When you choose the proper white balance for the color of light you are photographing, the color in the exposure will be neutral, and look correct. In mixed lighting conditions, where you have multiple colors of light, the light you white balance for will be neutral, while the other light will end up either too warm, too cool, too green, etc. In most cases, you will have one primary light source and color and if you want to keep your image color neutral, you will need to alter the color of your flash to match it. This is where color gels come in.