It’s been a while since I heard about this little tidbit of news, but about six months ago, Google had begun testing color variations for the reviews stars you would seen in search results. When you view the search results normally, you would see orange colored stars next to sites that used review rich snippets, but sometimes Google has tested different colors.
Google has decided to bump up the tests over the last week or so by showing mostly green stars as opposed to the orange/yellow stars. According to a spokesperson from Google, “yes, we’ve been experimenting a bit with colors there.” Adding, “you may see more experiments along these lines going forward.”
Here’s a picture of what you’re normally see:
Here’s a picture of the new green stars (sent by @WLau89):