I got to mess with some flash filters this weekend. I did this instead of cleaning (unfortunately)... some. The thing with flash is that it's color matches that of daylight, however, most of the times you aren't using flash in broad daylight. You're probably using it under fluorescents or tungsten bulbs, which are greener and warmer, respectively, than daylight. So, you fit a filter over the flash to match it's color to the room's bulbs and bingo, you have a match. Tungsten is a lot easier to match than Fluorescent since the later really varies from bulb to bulb (some are green, some are pink, some are blue). So this first shot is me matching the Tungsten colored bulb that's the main light in the room. With the camera's white balance set to Tungsten (this makes normal things blue and orange bulbs white) and an orange filter over the flash, we get a normal colored indoor flash photo. You can see how the super white fluorescent bulb in the back turns blue, but i'm colored correctly.
On the same lines, you can use the Tungsten setting and turn everything blue (like the sky or sunset) but still keep the person warm/normal colored. This one below started out like that (taken in daylight in the apt), but then i had a bit of fun altering the color curves to look like a type of film processing (cross-processing). It's odd how symmetrical I got myself. I know, it's not fun to look at me, but i like the lighting in this (although I'd like to soften the flash a bit more). And I really enjoy breaking the 1/3rd rule and placing myself dead center (although I'm not sure about the vaccuum in back).
And then finally, I just love this picture of Jess. Standing by the porch door using the light bouncing in from the snow. I love it.