I need to know when exactly WhatsApp messages are marked as 'read', so when exactly the blue ticks appear. I'll be a bit more specific: when I click 'Close' when I get a WhatsApp notification on my Apple Watch, is it marked as read? Or only when you're in the chat screen itself?
The tick mark appears BLUE as soon the recipient has read the message from the sender.
It will not be shown in BLUE if you clear the notification message. The person should actually read your message inside the whatsapp chat window, only then it would turn to BLUE.