1. Open main_style.css in your weebly editer.
2. Locate the code below.
border: 1px solid #000000;
3. The background color is indicated by background: #ffffff;
Depending on your theme the default Feature Area Background color may be different. The important part is to locate the background color code.
d) You can change the brackground color code (#ffffff;) to anything you like.
Note: In the event that you could not find the code in step 2, copy and paste the above code below the last line of the main_style.css and make necessary changes of the background.
Step4 : Save & Publish