Otherwise a black one, but shouldn't technically use a white one.
On the other hand if going to a local show, I wouldn't worry. The main thing is to jump a clear, otherwise the cleaning and polishing is usually pointless!!
this is me prepared for a working hunter class which should give you an idea on turnout - your horse can wear boots for the jumping phase but they need to come off for the show.
Pidges pic is a very good example of how to turn out for workers. Snaffle or double bridles are acceptable.
CotswoldSJ also hase a good point don't get too hung up on your turnout if its local. Just concentrate on jumping clear in a steady rythm. Easier said than done lol.