(edit) response to OP, before LaurieA posted!

No, that's not what it does.

 

It blends two different colour values according to the angle between the camera view and the surface 'normal' (an imaginary line pointing outwards perpendicular to the surface being rendered).

The "inner colour" is what it produces when looking straight at a surface (along the normal), and the "outer colour" is what it produces when looking along the surface (at right angles to the normal). The attenuation controls the transition between these values.

 

The edge blend "colours" are often just used as arithmetical values to control some other effect that varies according to the camera angle, such as reflectivity, or specular highlights.

 

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)