There is another test coming out of Google, a different style of filter buttons for their image search results. This format shows up on desktop image results for some people, and it uses different colored backgrounds to enhance the filter options to the searcher.
It was reported last August that Google started showing these filter buttons in the mobile image search results. In order to diversify, it now looks like Google is ttesting this on desktop, while also diversifying the background colors of the buttons.
Here is a screen shot that was taken by @WolfOfSEO that shows these filter buttons: