You have control over the background color of your email, as well as the background color of the content you include in your email.
To change any background color, start by heading to "Settings". There, you'll see that you have the options "background color" and "content area background color."
This is what they correspond to:
You can adjust the background color of your email and of the content area there. You can also choose the content area to be "Transparent".
I adjusted the content area color but my rows remain white. What do I do?
If you notice that one or more of your rows remain white, select the row by clicking on it. Then, adjust the "content background color" of the row in the menu that appears on the right.
It's also possible that your row has a background image. In this case, remove the background image in the menu that appears when you select the row, or change it as you please.