There will be rules for the show you are planning to enter. For the Horticultural show I attend, where there is a wine and beer show as well as plants, the rules for white wine are, as plumseverywhere said, a clear bottle, but not a cork, our judges prefer to have a plastic cap, as it is easier to remove.
I do know that some people use wine filters that have a very fine mesh. The result is a wine that has its original colour, but is much brighter.
Good Luck!