You can change the background color of each mail template.

Navigate to Email Customizer Plus -> Choose any email template.
Choosing background color/block color can be found under Decoration column under style section. 

You can either enter your desired color by providing the hex code.
Or you can choose the desired color by selecting from the color picker.

Choose your desired color and save the template.
You can check for preview by clicking on the Preview button.

Change color of each block :
​You can even change the background color of each element in a block.
Click on the block that you need to add the color for, and then you can see the background color section at the right.

You can choose the desired color by selecting from the color picker.

You can change the color of each blocks as per your requirement.

Quick Links:

Still unclear ?
Please submit a support request. We are always happy to assist you :)