Is it safe to eat white rice that turned blue/purple in the fridge?
From a bit of research, there is a bacteria called Chromobacterium suttsuga that is put on some types of rice to provide pest-control:


  The bacterium’s toxins can be combined with chemical compounds and then applied to soil, plants or seeds. To control soil-dwelling pests, rice grains can be treated with the toxins and applied to the soil, where pests will feed on the treated grains.


This source seems to be referenced in a lot of other scientific papers for agriculture for talking about Chromobacterium suttsuga and pest-control.  Some people claim seeing the discoloration on rice after a few days of being left in the fridge in a dark humid environment (like the bottom of a storage container where the discoloration appeared).  There are a few forums about this you can find by Googling "white rice turns purple".

For the question on whether or not it is safe to eat, since we don't have the tools to do any biological analysis to be certain it is Chromobacterium suttsuga in the rice I would recommend against eating it.  Even though the papers claim this strain of bacteria is safe to consume.

Source: https://aggie-horticulture.tamu.edu/extension/newsletters/vpmnews/mar04/mar04newdefense.html