I am setting up a WP site where people can register and post a question and other users can respond... I need to have a way to HIGHLIGHT certain users comments.

So I need a plugin that will let me specify these users (ex. user1, user2, user3...) and everytime they post a comment it highlights their comment in yellow BUT all other users comments look the same.

So do you guys know if a WP plugin like this exists? If not, know how to do it manually?

Any help is appreciated.