I have an email with a background color for the whole message. Per Litmus testing I was seeing that color being cut off on the right edge of the email in Gmail App (iOS) and Inbox by Gmail (iOS), so that the content extended out over the background color on the right.

I have a top-level containing table at width 100% with one td that contains and centers the content. That's where the background color is declared. (Well, it's email. The background color is declared in several places, but this place is germain.)

After much trial and error, I found that if I give a specific width to that td (100% didn't work) the background color will then extend to the full width of the client window. I put a class in my media query and the td to specify that width for mobile view, in my case width = 320 for a centered 300 content width.

As a happy aside, I also found that my content edges are now not abutted to the client window edges in the mobile clients. But most of you probably already know that (duh).

Hope this helps someone!