Recently, about 3 weeks ago, I colored my hair Rose Gold Blonde by Loreal. I liked the results although it was a little redder than I had wanted but now I want to go lighter with White Chocolate which is Light Ash Blonde, according to the box. My concern is that my hair will turn green or gray?

That could very well happen, especially if using drugstore box color a few weeks after previously using drugstore box color :)

It would be best to see a professional colorist.