You can change the message of the day formatting by using the Bukkit Color Codes
Let's say you wanted to make the message of the day red, and your current message of the day is "A Minecraft Server", you would change the message of the day to &cA Minecraft Server and then it would be red
There are also online tools for changing the formatting of the message of the day (Here is one https://minecraft.tools/en/motd.php)