The latest update to Apple's Mail app introduces a new set of colors for flags that are unique among the best email apps on the App Store. The problem is that they are hard to find. If you try to tag an email in the old-fashioned way, the default color is Orange, which does not seem to change. Of course there is a way, it's just a small evasive maneuver .
To find the new flag colors, you must first open the message. Then tap the answer button in the lower right corner of the display, and then tap Flag. Mail identifies the message as the default color orange, but it displays the other six color options: red, purple, blue, yellow, green, and gray. Tap the color you want to change.
These colors are only intended to help you distinguish your tagged emails. You do not sort your emails into separate folders. If you use another email app that supports flags, your tagged emails will be combined in one color. In the future, these apps may be updated to support cross-app color flags, but until then, you'll need to use Apple's mail app to get the new shades. The Top 5 Free Email Apps for Your iPhone