HN39,
Red, yellow, and green is needed. Red is means, "If' it's in this region and the plane is not resting on its landing gear then it is stalled no matter what." Yellow or perhaps orange means "You're stalled in this region if the air speed is above 60kts." That region gets adjusted for air speed. Green is "not yellow/orange/red" meaning you're probably OK but be paranoid if it's not neatly within the central region of green.
An AoA above 30 degrees is stalled. I am sure the 30 degrees can be set a little lower. In the case of AF447 any sane set of AoA display parameters would have been a clue. Whether the pilots would have had a clue what to do is up for grabs, after things that BEA said. Oy!
I rather wish they'd had words about AB's choice to shut off stall warnings with air speeds below 60kts no matter where the plane is. That's "bogus". It seems pretty obvious these pilots were not well enough aware of this counter intuitive trait.