Determine which color gels you need for your application. For color correction, if you need to transform a tungsten bulb to have a daylight temperature, use a blue gel (also called CTB). If you need to transform blue lights to match other tungsten bulbs, use an orange gel (also called CTO). To remove the green tint of many fluorescent lights, use lighting with magenta colored gels. For mood lighting, if you want a cool mood or imply daylight, also use blue. If you want a warm mood or to imply warm interior lighting or light from a fireplace or candles, you would use red, orange and/or yellow.
Slide the gel frame out of the gel frame holder. Depending on the light, the gel frame holder may be attached at the end of a lens tube that is inserted into the main light body or it may be suspended in front of the end of the light with a metal arm that is attached to the side of the light body.
Cut a piece of gel to the size of the gel frame. Place the gel frame on the gel sheet and trace around it with a permanent marker. Use scissors or an exacto knife to cut along the inside of the traced lines. The edges do not need to be perfectly straight.
Insert the cut piece of gel into the gel frame and reinsert the gel frame into the gel frame holder.
Aim you lights in the appropriate directions. For creating mood, you can light up a background, while still using plain lights on your subject. To create a sense of full light, use several floodlights, or lights with the shutters open and aim them throughout the space so that the edges of the light are overlapping and the light is diffused evenly throughout the space. For subtle, dim light, like that of a sunset or from candles, use just a few spot lights, or lights with the shutters mostly closed and aim them at low angles. For color corrections, aim the lights to fill the space and to create a balanced mixture with the other light sources. If you are using a flash, you may also need to attach a piece of gel to your flash so that it too will match the lighting situation. Attach gels to your flash with self-adhesive Velcro tabs. White balance your camera.