While testing the Network Namespaces, if you come across issues where you can't ping one namespace from the other, make sure you set the NETMASK while setting IP Address. ie: 192.168.1.10/24

`ip -n red addr add 192.168.1.10/24 dev veth-red`

Another thing to check is FirewallD/IP Table rules. Either add rules to IP Tables to allow traffic from one namespace to another. Or disable IP Tables all together (Only in a learning environment).