HI, 

I would like to have different types of activities, perhaps visually distinguishable.
ALERT, NOTICE, ACTION, WARNING

Maybe red for ALERT, white for NOTICE, yellow for WARNING, green for ACTION.

ALERT can be an alarm event that requires the user to take immediate action.

WARNING .. is what it means.

NOTICE is something like "An event has been canceled from your calendar," which I already have a power flow on.

ACTION can be something like a "free time" request that requires me to take action, maybe deny or approve 
..

Regards

Reinhard