how to call for rgb vertex color in unity?

Thanks a lot, but am still a little confused. Am trying to change only the scale of the blue vertices, but I don´t get how.

 void Update ()
 {
     if (Input.GetKey (KeyCode.T)) 
     {
         if (color (0, 0, 1, 1))
         {
             this.transform.localScale += Vector3.one;
         }
     }

This is just an example and I know it´s not achieved this way (because it doesn´t work), but is more or less what am trying.