The world turns Gray with the mingling of a great many thoughts.... I can't allow it to happen. Pokemon and humans should be cleanly split. As clearly seperate as Black and White.
Could the word Gray in this phrase refer to Kyurem and Pokemon Gray Version!
The word gray in that context refers to non-polarisation of the 2 extremes in the world (human and pokemon), a "gray area" if you will. It's not a Kyurem reference, just as how the words "black" and "white" in that sentence are used metaphorically, not as references to Zekrom and Reshiram.