You can set the threshold values for green and red (and everything in-between will be yellow). Also, you choose whether high values are good or bad.
Since the item itself is a regular Apex item, you can assign a value to it using a computation, process, PL/SQL expression, etc.
The icon is displayed using Font Awesome (bundled with Apex). The value is displayed as a tooltip when you hover over the icon.
Download the plugin here.