What color flash diffuser do I use?

I bought three plastic flash diffusers for my Nikon D3100 and I was wondering which one do I use depending on where I'm taking the shot. I have white, blue and orange. I need help on what's the difference between them and when to use which.

White most of the time.

The blue is used in deep shadow

The orange is probably 85b, so would be used to match the flash to incandescent lighting.

Usually the colored filters are used to counter existing lighting or enhance it or for special effects Example: an orange filter with fluorescent light eliminate/reduce green; A deep orange filter on the flash and deep blue on the lens to make the foreground subject look 'normal' and the background look bluish.

BTW: Filters are for fun and experimentation most of the time. Only some (Skylight/Haze, Polarizer, UV, infrared (IR) and some others) are for a specific purpose.So, experiment and have fun!

Hope This Helps.
Good-Luck!

None of them. The major effect of a flash-mounted diffuser is to reduce the reach of your flash. Most of the time when you're using the flash, you're going to get some effect from ambient light. It's seldom a clean source unless you're shooting in daylight. So adding another wavelength modifier like blue or orange is just going to make things more complicated. A better strategy would be to shoot in raw mode and correct the white balance in post processing.

Diffusers are one of those topics that elicit die-hard opinions. You'll get lots of folks who disagree with me, mostly those who make money selling them or have bought the line. Others agree with me. Take your pick.