I actually don't use white, I use black stripes on the court or chairs to set my WB.
I shoot at speeds between 1/1250 and 1/2000, if possible. In high school gyms, I have to slow it down a bit because their CFL and gas lights are too dim and I end up at ISO 16000, like the below sample. No flash either, as there is no good place to put flash around the court, and having it on camera just won't be sufficient to really change anything. The colors are dull when I do this however and it takes a bit of post to bring them back a bit.