The question i ask you!:
What for model/brand/speed memory are you using?
Maybe the problem only occur with certain ram modules since the Intel GPU is using the system memory.
I am using Samsung 1600Mhz 2x4GB. My system reports that it is utilizing all 8GB of total RAM, operating at the full 1600Mhz. It is a 2012 i5 Mac Mini, and I do suffer from the black/snow problem, usually when the HD4000 is being taxed (such as when gaming, or video processing).