How does Android dual-card dual standby judge which card sent the message?

First, short messages on smart phones are generally in the form of conversations. You can go to Settings-SIM card management-and you can see what colors the icons in front of the two cards are, such as blue and red. Then, if you enter a short message, you can see the background color of the conversation, which corresponds to the status color of the card.

Second, there is a distinction between card 1 and card 2 in the lower right corner of the message.