This brings about an interesting question about signalling in different cultures. In the Western world 'green' generally means 'up' or 'positive' whereas 'red' signifies 'down' or 'negative'. In many Asian cultures, China in particular, it's the other way round.
Therefore it's quite funny when Western media talk about stock market declines in China and in that context regularly display stock photos that show all stocks in the red.
I'm not sure if this applies to notifications, too ('green' meaning 'positive' and 'red' meaning 'negative' or 'urgent') but it's certainly something to keep in mind when designing an application that's intended to be used by people from different cultures.
