Ginger didn't used to be blue/green on the inside. It's not from going bad. I've had plenty of experience with ginger going bad. It never turns green/blue inside. Now all the ginger I get from the store is that color. The color reminds me of the color of various copper compounds, and I'm worried that it's a new systemic insecticide or something.
The only blue ginger I've ever heard of is not actually ginger. It is in the Commelinaceae family, not the Zingiberaceae (ginger) family. The blue refers to the flowers: http://wildlifeofhawaii.com/flowers/467/dichorisandra-thyrsiflora-blue-ginger/
I grow Alpinia galanga, or Thai ginger, and it is not blue inside either. It smells and tastes different from regular ginger. I still want to know why the ones the stores are now selling are green inside.