I mean, they've existed for a while, I've just been trying to clean them up. Most boorus I've seen have them (like Derpibooru for example) - it's not like color body part tags, something like background color is a big aspect of the image and if you're looking for a specific image you remember, it can be a piece of the puzzle.
Also, simple background is helpful if you're looking for images with a solid flat background that can easily be removed.