Following are the steps to change the colour of the user name.
To change user name:
1. Tap on Settings button(a gear button) on the Home Screen.
2. Tap on Change in front of Nickname to change username.
To add colour:
1. To add colour visit the following site https://htmlcolorcodes.com
2. Add colour code in front of your username.
3. eg: [FF5733]Username