The Gemara (Sanhedrin 97) says that Moshiach will come when every government in the world turns to Apikursus. Rava says, "We see it from the pasuk (Tazria 13:13) 'Kulo Hafach Lavan Tahor Hu;' when a nega spreads through a person's entire body he is tahor." What is the connection?
Rav Shamshon Rephael Hirsch says that white is a distinguished color, the color of purity, righteousness, and innocence. It is the color of a special breed. When every country turns to Apikursus and cloak themselves in righteousness, only then will Moshiach come and spread true purity on the world.