Stealth settings provide you more control over your time, by allowing you to choose the people who see you as online and offline.
If you are IMing with a few people and don't want to be interrupted, you can
use Stealth Settings to appear invisible to everyone except the people you want
to talk to.
If you want to go completely Stealth and hide from all your friends, you can use the "Invisible to Everyone" status message.
Here is a example your Status is Available
You appear offline only to Becky and Jessica,
and online to everyone else
So, only Becky and Jessica show in Blue
Becky and Jessica
show in Blue as they have had Stealth
Setting applied to their usernames
Changing Stealth Settings on Yazak for a username
ie Becky Chapman
More Yazak Help