Lighting a basketball court sized gym floor....

[suemccartin]

Hi All
I've kind of become the unofficial photographer for my karate school. Fast action, low light and worse yet....ambient light of a different color than daylight.

The first batches of pictures I took in the one big gym (basketball court sized) came out with horrible deep yellow backgrounds--would like to find a way to fix that problem (I can't seem to find a way to fix it with any of the photo editing software that I have).

My canon G2 in the same gym didn't have that problem with a 380EX speedlight, but for whatever reason my Rebel with a 550EX is having this problem. I thought perhaps I needed to set saturation down, pictures shot in a different gym with the saturation down and the iso at 800 don't have the yellow background problem.....however I also suspect there's a different kind of lamp in the smaller gym which is closer to daylight than what's in the big gym (and I'm also closer to the subject in the small gym).

Settings:
Tv Mode: 1/125 + selected
ISO 800
550 EX set to high speed sync
Parameters: Saturation Normal, Contrast Normal--other two set to max

It's been suggested to put a yellow filter on the 550 and manually set white balance so all the light is the same color....which makes a lot of sense but the filter is going to mean I have to boost the flash output a half stop and I'm worried the flash is going to be slowed down so much it won't be able to keep up in continuous mode (which is an issue I'm having because I've got f4/5.6 glass and nothing faster). I've got the cp-e3 battery pack for the 550 which has helped a great deal but I still have problems with the flash keeping up with continuous mode sometimes.

I was wondering if anyone could give me some ideas about stationary AC or battery powered slave flashes or lights, how do I figure out how many I need? Next question is of course positioning. I'm thinking one at each corner and perhaps one in the center on each side. The 480EX speedlight is the cheapest slave but I kinda doubt it can keep up with just batteries and there's no external power socket on that unit. Thanks for all the help.