Some theory first …
Light doesn’t come in one color. Ever noticed how things look more yellow under a light bulb, than under the sun? It’s because the two produce a different color of light.
And if you’ve done a photo or two before, you’ve probably noticed how they look very orange indoors, under a light bulb, but much whiter when you turn on the flash. Different colors of light. Flashes, they have about the same color of light as the sun. It’s what we’re familiar with, so it looks white. But we don’t always want it white. Maybe you want to color that flash the same as a light bulb? Or green, for a special effect? This is where gels come in.

I bought myself a Lumiquest FXtra, for some color. And as with everything new, testing it was inevitable.

A great thing about gels and photography in general is, you don’t need to make it look real. You don’t always need to make things look real (and light look white).

I’m living with a fluorescent light bulb above my head. It’s stated as being “neutral white”, but my camera doesn’t know that.

I equipped my flash with a CTO gel. CTO means orange, about the same color as a standard light bulb. So I convinced my camera this CTO was white — I shot a gray pillow and set custom white balance to that gray. In contrast, the white fluorescent turned blue all of a sudden. Which was exactly what I wanted.

Click, in my face.