In order to overlay a colour on top of a background image, you'll need to set the following custom css on your row:
box-shadow: inset 0 0 0 1000px
To do this, follow these steps:
Step 1: Edit the Row Styles
Step 2: Open Backgrounds and Colors and use the color picker for the Background Color to select the color and opacity you want and copy it
Step 3: Using the above provided css, and the color you have chosen, set your custom style under Custom CSS and click OK
Step 4: Profit!