Redmine

Hi everyone,
currently i'm looking for an option, to color users depending on their respective roles.

So we can identify on a glance if we have for example a new user, which would not recieve mails when answering a ticket.

How should i go about it, is there a plugin enabling this, or would i have to use custom CSS?

Or is there another way of catching, that a user would not recieve a mail?

Best would be a popup when opening the ticket with the edit button, or a message getting displayed in the edit field, if a user (and/or watchers) would not get a mail.

Is there a plugin like this already, or what option could i look up?

Thank you.