in the application i'm working on, there are 2 types of notifications: Confirmation messages (successful action results) and Alerts (unsuccessful action results/errors and Session expiration prompts). It was decided that messages would have a similar look to Gmail:
Confirmations would be dismissed in 3-4 seconds and Alerts would have to be acknowledged and closed manually.
Would it make sense to distinguish between Confirmation and Alert messages - using either color, animation or icon? For example, yellow for confirmations, orange for alerts and red for errors.