Active tab state

I found myself confused today using the Adobe Reader Android application when navigating it's tab interface. I wasn't sure which tab was active becuase the active tab state was recessed and dimmed, which led me to this question.

In general, when a tab is in active state should it appear forward/brighter/more colorful and or more prominent than the others?

Also, are there some rules of thumb, for the UI treatments of Tab states.

I am not a designer so I am sure there are some better terms to describe what I am taking about.