Blue tick in Whatsapp means the message is read. You sent a message to someone. When the message takes the form of double click and blue, it means that the other party is reading your message. Some people can turn the blue tick off. You can do it too. This method is used to hide whether you are online or not. Even if you read the message, the information you read does not go to the other party. When you turn this feature on, you can't see if anyone has read your message.
This means that it is a method to be used to understand that the person is reading your messages while texting with you even if the blue tick is off. You can see the blue tick when messaging with you while online information is off to other people. So you can understand that you have read your message. There's only one method of doing this.
Blue tiki may be your lover you want to see. Or a colleague with important messages. So if you want to see someone's blue jacket, all you have to do is set up with him. Just as you two are in the same group messaging normally, but you only have two. In this case, people will not be active in the group even if the blue tick feature is turned off.