1. Go to the "Settings" menu.
2. Write your message in using the format color code : §2Hello §6Minecraft §6Worlds §6!!
3. Click on "SAVE CHANGES".
4. Restart the server.
Here the formatting color codes:
You can check the message from your Minecraft multiplayer menu.
§2Hello §6Minecraft §6Worlds §6!!
If you want to make two lines you need to use this symbol §§ :
§2Hello §§ §6Minecraft §6Worlds §6!!