Compatibile with iOS 7 and 8
Highlight emails in the Stock iOS Mail app. The highlight can be based on account name or filters can be added to match the email Subject, Sender and/or Recipients. This is the freeware version that is meant, basically, as a trial for the full version. It will only let you select one mail account to be highlighted and apply two filters. The full version, Mail Labeler, allows you to select different colors for each of your mail accounts and has no practical limit to the number of filters that can be applied.
Configure options from Settings.
See larger Screenshots below..