I have a number of email accounts so that when reading an email it is easy to lose track of which account it's from. I have to glance at the folder list and ensure the top folder (which account name) is shown to confirm the account. To make things easier, it would be nice if a custom header theme could be used per account, e.g. a blue background one personal and green background one work.

I suppose this would make more sense if a number of variations on a theme were provided, such as fancy headers, or if there were some configuration settings where one could choose the background color of a particular header theme to allow minimal customization.