Does anyone know how I would go about changing the colour of the text in the Number column based on if the ticket has gone over the SLA or not?
Around here: https://github.com/osTicket/osTicket/blob/develop/include/staff/tickets.inc.php#L529You can use this to see if the ticket is overdue or not: $TSo if positive add the css style color:#FF0000; for example.
You might be able to get away with:.overdueTicket { color: red;}But that only changes the subject text, not the ticket-number text.