Did you follow the steps in the directions for MacOS in the links provided above? Particularly step three and beyond?
In order to connect to the My Cloud you need to log into it with SSH using the My Cloud’s IP address. If you do not know the IP address of the My Cloud then access your local network router’s administration page to find what IP address the router’s DHCP handed out to the My Cloud. For example if the My Cloud’s IP address is 192.168.1.10 then you would log into the My Cloud via SSH by issuing ssh firstname.lastname@example.org (v4.x firmware) or email@example.com (v2.x firmware) in the Mac OS Terminal window. Then enter the SSH password. Once connected then one can issue the various commands to change the LED color.
Using SSH requires some knowledge of how to use the terminal window and how to issue Linux commands. If you don’t know howto do so there are plenty of instructions and how-to guides to learn from. One can use their favorite internet search engine to find various blog posts and videos on how to use Mac OS Terminal and how to access a device using SSH.