My Ubuntu Looks Like This:
Why are the icons showing up as black and white?
You are using the hight contrast theme, open your Apearence setting and change it back to Ambiance (or Radiance).
What you are seeing is a THEME called high contrast.
Right click on your desktop and set it to ambiance.
N.B. The high contrast setting toggle is no longer in the screen appearance dialogue under my 22.04 Ubuntu. The advice is correct, high contrast is causing the b/w icons. But the toggle is now in a new place, that is, it's found in universal access. I kept poking around the old dialogues where it no longer exists!