Not sure what the 'green' is, it sounds like you've accidentally activated some kind of lo-fi or light skin mode.
Down in the bottom left there's this drop down, you want to select "Anime OTK original" from that drop down and the page should go back to black.
The site itself hasn't had any changes, it's either you've misclicked on this setting or something on your browser it changing the way it displays the site.
