The Samsung messages app is RCS compatible or capable. Your carrier is also running a RCS network infrastructure.
The messages app scans your contacts and connects to your your carrier database and determines how many of your contacts are using RCS capable phones and their RCS network infrastructure. It marks the contacts with a blue dot if they have met the requirements for sending and receiving messages in chat mode.
You should be able to send and receive multiple large image files at full resolution. Also uncompressed video files and your text messages character count limit should go much higher. When you send mms and text messages to contacts without the blue marker the messages app will send and receive mms and text messages using the standard messaging format.
Edit Oct 5th, 2020
My carrier T-mobile in partnership with Google has implemented RCS Universal Profile. This opens up a lot of new contacts for chat messages with friends who are using Googles jibe network. The original goal was to have Interoperability between all the carriers using Googles jibe network infrastructure. Some carriers signed on right away while others created their own proprietary chat networks. I was originally only able to chat with contacts using the T-mobile chat network but today that has all changed for the better. We still need a few more of the major carriers to join in so we can all use chat messaging regardless of which carrier we're with.
why does the blue dot turn green sometimes
My dot is sometimes green and sometimes it's pink. I don't really understand all that talk about RCS anyway and should I have to. I just want to know if I should just ignore the dots.
How is it my wife and I have same phone same carrier as well as my son theres always a blue dot by my sons contact in messages but not my wife's?
Yes, but, the ones with the blue dot also show me when that person has read their text msg. The ones that don't have the blue don't don't show tis.
Is this for the same reason?