PBase

i have a band promo shoot tonight and want to use this technique.

i want to put a slaved flash behind them with a colored gel on the head to light up the wall behind them.

got any tips on expsure? setup? etc?

think ratio.
think grey scale.
test it before you have to shoot it.
use a meter and write down every measurment and meter reading like dean did a long time ago.

If possible find a black wall and not a white one because the color will be more vibrant on black.