Those icons are for "available for chatting"
We do have red circle on the name if they're on a call. Blank if available via anything, user portal / app/ desktop phone etc.
Actual status can be seen from under the registration tab as to what they're registered via. If the user is registered via an app and not via the desktop phone and adding a gray color for that can be confusing. We've kept it uniform, the colors are only for chat availability. For calls, if they're not on DND (DND symbol) or already in a call (red circle), they can be called.