You get to see these by pressing the Alt key. Pressing it again (or Esc) will hide them.

These are another set of keyboard shortcuts. They were introduced in Office 2007. They allow you to maneuver in the Ribbon using the keyboard. (In Office 2007 and 2010, they did not have the black background but rather were in little boxes.)

If you get to the print screen by pressing Ctrl+P you should not see them.

BTW, the shortcut to get to the open screen is Ctrl+O. Your picture was of the File Open screen.

And no, you can't turn them off. They've been a part of Office for more than a decade now. I've learned to avoid the Alt key, or rather to only press it as part of a keyboard shortcut very quickly. These can be handy if you pay attention to them. It makes it easy to use ribbon controls from the keyboard. Like you, I mostly find them a nuisance and try to avoid them.