Why Has My Adobe Illustrator Gone Black and White?

You probably entered outline mode. The shortcut for this is Ctrl+Y, or Cmd+Y if you’re on Mac. This shortcut will enter the mode and exit the mode for you. If you save your work and close Adobe Illustrator and then reopen it, it will still be in outline mode.

Outline mode looks like this:

Outline mode is really helpful for certain situations. It allows you to view your vector paths with no effects on them, so you can work with a lot more precision. It also allows you to easily access objects that sit behind others.