Try moving the cursor slowly just above the Default Appearance: color. If it changes to an icon with a pair of horizontal lines with opposing vertical arrows, click and drag downward.
hovering above the words "Default appearance: Colour" was indeed the required stroke of genius
and one drag later all is restored to its former state.
I have no idea how on earth anybody uninitiated was ever going to guess that was the required move...
hmm perhaps a GUI not quite living up to the principle of least surprise
At the point where you clicked and dragged, there should be a line similar to the one below the yellow box. It is not showing in your posted image.
Are you using a certified/approved video card?