A codeshare flight is when the marketing airline attaches their own unique flight number to a partner flight. The reason why AC6229 displays a star alliance logo is because AC has their own flight number on it, and since they are alliance partners, they display the *A logo.

NH269 has the blue plane logo because AC does not have its own unique flight number on it (or at least is not the option). A blue logo just means that they are a partner of AC (*A or not), but the flight is not an AC-coded *A partner flight.