RCS or Rich Communication Services is a new method of messaging. It is a replacement to SMS that supports high resolution media transmission, can see indications the user is typing, only needs an Internet connection to use it, has high privacy and security including encrypted messages and more.
RCS can be used on many Android devices now, among the apps that already support it are Google Message and Samsung Message. It can be said to be a service similar to iMessage, but it is universal and allows all Android devices to be used without following the brand.
Google has long recommended to Apple to integrate RCS support on iMessage and not use their own system. Although iMessage has the same features and functions as RCS, it can only be used among Apple users. If an iPhone user sends a message to an iPhone user, the text bubble will be blue. But if sent to Android users, it will be green which means SMS is in use.
Google recently used Drake’s new song Text Go Green from the album Honestly, Nevermind to mock Apple for integrating RCS on iMessage. This song means the text on a received message turns green on iPhone users when other users block via iMessage.
According to Google, only Apple can do this and only their talented engineers can fix this "problem".