Welcome to the wide world of gels! First, some background and definitions.
Gels are thin plastic sheets available in a variety of cut sizes and rolls, and a huge array of specially formulated colors that yield unique and repeatable results. They can be used for both creative and corrective effects, and they work with strobes, speedlights, constant lights or a combination of sources. The variety of gels and their uses is huge, with anything from simple to the wildly fun and experimental, and everything in between.
It Ain’t All Colored Plastic
Cut sheets and rolls of light-modifying materials don’t stop at colored gels. There’s an entire range of diffusion fabrics available as well. These help soften light to give it any of a number of different characteristics. Products include fabrics like Tough Spun.