The command syntax is:
/mode #yourchannel +b r:realnamehere
Remember spaces and colours and any hidden characters should be replaced with wildcards * or ?.
For example if someone has coloured realname like: Hello my name is tata.
In this case as you see a lot of colors, you will have to replace each colour with a wildcard.
ie: /mode #channel +b r:*hello*my*name*is*tata.*
As i just used * wildcard for each colour and spaces.