It looks like Google is testing a more empty style for its search bar. The search bar has no apparent box to enter your query after your query is in the box (that you don’t exactly see). It also changes some of the icons to gray without color.
Here is a screenshot of the empty search box Google is testing (click to enlarge):
Compare that to the normal search box, that has an outlined box and a colored microphone and search icon:
But in this test, the search bar is not always empty looking, it turns empty after some queries are entered. Here is a GIF from Praveen of this in action:
Brodie dives much deeper into all the variations of this test over here.
Note, this seems to work with the new full width auto complete menu.
Forum discussion at Twitter.