Navigate to Administration | General and choose Trigger displaying options in the drop-down in the upper-right corner:

It's not just trigger severity labels that we can modify; we can even change the default red and green colors, which are used for the PROBLEM/OK states. Even better, the color can be different, depending on whether the problem has been acknowledged or not. We discussed trigger state blinking in Monitoring | Overview and other frontend sections for 30 minutes. On this page, we can selectively enable or disable blinking based on the trigger state and acknowledgement status, as well as customize the length of time for which a trigger change is considered recent enough to blink. The default can be seen here, defined in seconds: 2m. The Use custom event status colours option allows us to turn on the customization of colors for acknowledged/unacknowledged problems. This option was added in version 4.0.