Is there a device that can measure the color of the light so I can know which gel to use on my flash? I have a pack of gels but it's not that accurate to just choose by eyeballing the color of the ambient light.
Light meters only measure the intensity not the color right?
You could use a digital camera to improve accuracy of eyeballing. Set its White Balance setting to "flash WB" and take a picture of a custom WB target (a gray card, white paper, bride's dress etc), without actually using flash. Switch the camera to playback that picture, and find a gel from your pack so that the WB target, viewed through the gel, looks the same tone as the playback image on camera viewed without gel.
Remember to adjust WB setting to match the ambient light afterwards, even if you shoot RAW.
There are colour meters, like the Sekonic C500, but they've never been cheap. Even a used Minolta will set you back a bit. And they're far more accurate than you really need; a few 10s of CC difference between ambient and flash doesn't make enough difference to warrant the trouble unless you are working on something that is truly colour-critical (like commercial branding).
