Android : Do we have to differ the color of status bar and the action bar for android 5?

I peeked through some apps which are somehow optimized for android 5, and I noticed that the ones which have Action Bar, and have a specified color for status bar, have differed those two color. for example in Twitter's Official client, The status bar color is #1c6399 while the color for action bar is #55acee or in "BBC News" app, the status bar is #660000 while the action bar is #990000. Is there a rule behind this? I mean OK, I find it more reasonable than making them have the same color, but how do I reach that color? for example my action bar color is #6e97b9, what should be the color for my status bar? and in general, what is the rule behind it? or is there any?