...
Hover over the wrench icon on the right side of the row and click Edit Row.
Click on one of your columns, anywhere but in the middle where the percentage text is.
An additional section will appear in the right sidebar below Row Styles called Cell # Styles
Under Cell # Styles > Design > Background Color change the color for your column
*You can also add padding and any other additional styling from the Cell # Styles section
Save/Update the page
...