Here is how to highlight the string noodles in the output of tail -f using grep:

tail -f /var/log/auth.log | grep --line-buffered --color=always -e "^" -e "noodles"

Figured it out quickly thanks to these posts:

• https://superuser.com/a/1192944
• https://stackoverflow.com/a/7162898/1198249
• https://stackoverflow.com/a/23395752/1198249

There is also other (possibly better) ways to accomplish the same effect:

• https://unix.stackexchange.com/questions/8414/how-to-have-tail-f-show-colored-output
• https://stackoverflow.com/questions/14691680/colorize-tail-output