Joke Collection Website - Public benefit messages - Why is the message received by the 4s mobile phone in black on a white background, but when I reply, it is in white on a blue background?

Why is the message received by the 4s mobile phone in black on a white background, but when I reply, it is in white on a blue background?

Explain that the other party's mobile phone is not an iPhone. When you reply, it displays white characters on a blue background, indicating that it was sent in the presence of a network. By default, it is sent by Apple's iMessage, and the SMS fee is not deducted. If there is no network, it is sent in white on a green background, which is a normal SMS. If both parties are iPhone, the default is to use iMessage to send.