Gels are simply colored translucent plastic sheets that can be placed over lights to give color to the shot. They are available in many colors. In the shot above, I used a teal gel behind the model and an orange gel in front, and accentuated the effect by using fog as well. Teal and orange are complementary colors…that color wheel comes in useful when picking combinations. A shot like this one is more likely to be useful for social media than framed on Mom’s wall, but it is a fun and different look.
A bit more subtle is the shot at the right with the same gels, but less intensity. This becomes a bit more traditionally usable photograph. I like the teal in the shadows and the warmth imparted by the orange gel, but it looks much less alien when the intensity is modulated.
Finally, the last shot used only the orange gel and that was not strongly present. If you back the light away from the model or turn down the power on the flash, you can reduce the strength of the effect. That makes for a much more traditional coloration.
Don’t hesitate to try gels. You can get them at large photo supply stores or on line and they work with any flash or light source. They are inexpensive and a fun accessory. You can use them to go wild, to color a background wall, or for just a hint of color like the final photo here.