På blått

Writing “på blått” means using the chat function on Snapchat. The name is Swedish and directly translates into “on blue”, because the chat icon is blue when a person has received a new snap. The use of the word started in Kungälv, Sweden, but was spread to the large city of Gothenburg by student Matilda Martinson.

“He wrote to me på blått”
”Wow, he must really like you”