Doesn't say really....Here is their rule:
"Shoes are worn to accentuate the calves and can give the illusion of greater leg length depending on the type of shoe selected. Shoes should not be virtually the same height off the ground at the toe as they are at the heel, as they would fail to accentuate the calves. Shoe color is up to the competitor, but please note a clear shoe tends distract less from the physique. Shoe style is up to the competitor also. Competitors should choose a shoe style that compliments their physiques. For example, if a competitor has a long upper torso, perhaps they will choose a shoe with a 6" heel and 3" height off the ground at the toe to give the illusion of longer legs. Excessive heel heights (ex. 5" difference between the heel and toe height) should not be worn if they present difficulties for poise, elegance, and stage presence as this would result in the potential for lower placement. Generally, competitors choose a clear shoe with an inch of height or less under the toes, but this can vary depending on the illusion a competitor wishes to create."