This thing is part of vrayScatter plugin (http://rendering.ru/) it's called vrayScatterTexture:
Here's screenshot:
http://img144.imageshack.us/img144/6692/scatdd9.jpg
Basically when you assign material with this texture two many objects (instances or not , doesn't matter) it scatters on all of them so each square color goes to each object.
Would it be complicated to write script that will do same exact thing?