Messenger Plus! adds codes in your name that symbolise the colour. These codes can only be read by Messenger Plus!: if you have Messenger Plus! installed, and it finds a code like that in your name, then Messenger Plus! knows that it should change the name into that colour.
If you do not have Messenger Plus! installed, then there is nothing that knows that the codes in the names of your contacts mean that your name should be in a different colour. It is Plus! that recognises the codes and changes it into the right colour; if you do not have Plus!, it will not be in colour.
Colours only work if your contact also has Messenger Plus!, that's just the way it is
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