14 STEPS
1. Open your Google Slides, select your desired slide you'd like to change, then click Slide.
2. Click Change background
3. Click Color
4. Select your color. We will choose red berry.
5. Click Done to finish the color change.
6. Click Image if you want to insert and image as a background
7. You have six options from which to pull a picture. We will use Google Image Search
8. Find your desired image
9. Click Insert 1 item
10. Click Done
11. To undo, click Change background
12. Click Reset to theme
13. Click Done
14. That's it. You're done.