When do the messenger's face on my adress book return into yellow,and when it's grey what does that mean?

because allah wills it this way.

When do the messenger's face on my adress book return into yellow,and when it's grey what does that mean?
if it is yellow their online if its gray their offline
Reply:if its grey they arent online if its yellow they are online
Reply:In general, when you're on-line the face is yellow. When you are off-line, gray.
Reply:When it is yellow they are on line...Grey they are not
Reply:yellow means we are in action grey we are..... ooops!!!!