Green and black snow falling on polluted Russian towns has compounded rising environmental protests that are chipping away at President Vladimir Putin's ratings.
The bizarre phenomena triggered demonstrations against unscrupulous polluters, including a coal processing plant that turned snow black, a chrome factory that turned snow green in Pervouralsk, and a burning copper and zinc mine that has inundated Sibai with smog since November.
It comes after a series of separate protests against plans to export Moscow waste to the regions.
Authorities raided the homes of activists in late January before public demonstrations.
Among those raided was the flat of Vyacheslav Yegorov and his family in Kolomna, 95km south-east of Moscow, one of the many cities importing Moscow's waste for processing.