How to add blue dot to list of unread messages in Mail

[elasticmedia]

I have my Mail set up on my iMac and each unread message shows a blue dot, helping it visually differentiate from the read messages. Sure they can be bolded too, but the blueness is really helpful.

On the other hand, my macbook Air doesn't have the blue dot and I can't figure out how to turn it on in the preferences.

Both computers are running Lion OS.

Thanks for explaining the solution.


Jim