UIActivity represents an icon that appear in UIActivityViewController's view. (the iOS 6+ share menu).
You can force a custom activity to appear before another activity by returning the other activity's type string in the method:
You must also return YES in
If you return an image from the method -[UIActivity activityImage] the alpha will be used as a mask for the metallic grill background. In order to have a fully custom full colour icon return the image from the method: