First, why do we blush? The feeling accompanied by blushing is an exquisite sensitivity to the feeling of embarrassment. Embarrassment is often tied to shame. Blushing is an automatic, uncontrollable response to these feelings. It happens in humans because our facial veins react to this adrenaline. So when the limbic system is triggered, the blood rushes to the face causing the redness to appear. There is a lot of basic (scientific) info on this reaction here, here and here if you are interested.
But what you really want to know is how to control blushing. Right?