Google is testing a different style of filter buttons for their image search results. The new format shows up on desktop image results for some and uses different colored backgrounds to enhance the filter options to the searcher.
Last August, we reported that Google began showing these filter buttons in the mobile image search results. Now, it appears Google is testing them on desktop and also diversifying the background colors of the buttons.
Here is a picture from @WolfOfSEO, but others have seen this, as well: