She's got Leggs and she knows how to use them

Kate Middleton's affection for iridescent colored sheer pantyhose might be more a party of protocol than her own choice - it's considered part of royal protocol (albeit an unwritten rule) to wear hose within the palace and in front of the queen, especially when on royal assignments.

Regardless of the reason for Kate Middleton's choice, she's sure has made a change in the fashion during her tour of Canada and US by completing her outfits with the prettiest, and sheerest pantyhose.

source:  http://www.squidoo.com/sheer-pantyhose-the-newest-fashion-craze