Hmmmm -- this doesn't sound good:

...Snow ranging in colour from light yellow to orange and carrying a distinctive "musty" odour was observed Wednesday in five districts of Omsk province, which lies in western Siberia and borders Kazakhstan, ITAR-TASS said.

"Residents are advised not to use snow for their household or technical needs and to limit walking, either by people or their pets, in this area," the official said....

The Omsk province is known as a centre of the oil industry and the provincial capital is among Siberia's largest cities.

Ah, but I'm sure that even if a panel made up of scientists and representatives of more than a hundred governments were to conclude that human activity changed the color of this snow, we'd be assured that we were falling victim to a massive propaganda assault, and multiple Drudge-touted books would assure us that it was all perfectly natural. Those who detected the involvement of humans would be compared to Osama bin Laden. Maybe the American Enterprise Institute would even try to bribe scientists so they'd say it was perfectly natural.