Currently backgrounds are not available for Recognition Ads. You can add background color to your ad by using an editable shape.
1. When editing your ad, select Graphics.
2. In the dropdown, select Editable Shapes.
3. Select the square and drag it to your ad.
4. Click on the square and Shape Options will open. You can change the color of the square now or after you resize it. Select Options and Color.
5. Click on the color square.
6. Select the new color by moving the two circles to find the color you want.
7. Click on the square and use the editing circles around the square to stretch it to fit your ad.
8. When the ad is covered with the color you will need to move it behind the content in the ad. Click on the square and use the Backward button to move it behind the content.
9. You will need to keep clicking on the Backward button until all the content has moved to the front of the color.
Suggestion: You can also try other graphics to add to your ad and move to the back as a background. In All Objects search flower. These will make a nice background for your ad.