What does the letters S, Grey D, Dark D and R, mean in kik?

Some people say that it will be Dark D until they open the app. Does the app have to be open or can they just be on there iPhone and still not opened the app for it to be Dark D?

S means the message has been sent to kiks server
Grey D means that its been delivered to there phone and they haven't opened the app yet
Dark D means that they have opened the app
R means that they have read your message