Several different companies make gels and filters for professional studio photography but the name of Rosco is known worldwide. Rosco makes several hundred different classes of color correction material. We recommend you start with their Rosco Color Correction Kit, which includes a range of 16 color correction filters, each 10x12 inches in size. These are the key essential filters that you need to improve the quality of your lighting.
Rosco makes neat little sample swatches, one for calibrated color "CalColor," the other is a set for Rosco Cinegel.
Several other companies make comparable products, but the brand name of Rosco is the equivalent of the Hasselblad and Leica of lighting gels.
It is not always easy to get electricity that gives the correct color temperature, so it is essential to have color correction capability available. If you are photographing Maya jade artifacts, their color will look rather strange unless the color temperature of the lamps is corrected.
With digital photography you can make the corrections with the software, but with tungsten lamps you have to correct the color from the source (and/or on the camera lens).
This Rosco product is essential for anyone using tungsten lighting.
Buy a roll of the black, or the white, cinefoil.
After you see how helpful this product is, you will wonder how you could ever have photographed without it.
You can buy products of this nature from Calumet Photographic and elsewhere.