An Identity-key mainly shows the state of the registration it is set up for:
solid yellow: identity is disabled or otherwise not working/registered
yellow blinking: identity is trying to register
off: identity is registered but currently not selected as default for making calls
solid green: identity is registered and currently selected as default for making calls
Pressing an identity key once will select that identity as default for making calls. Pressing a selected identity again opens the dial screen
The current template itself for this key-type can be found here.
The key-type has the following parameters:
Which identity this key monitors.