Open a presentation, then .
Next to Text Background, click either the color well on the left or the color wheel on the right, then choose a color.
The color well shows colors that match the theme you’re using. The color wheel opens the color window, where you can choose any color.
Next to Text Background, click the color well on the left, then click the swatch in the bottom-right corner with the diagonal line.
Use this method when you want a block of color behind paragraphs.
Go to the Keynote app on your Mac.
Open a presentation, then select the paragraphs where you want to remove the background color.
In the Format Apply a paragraph style in Keynote on Mac