turn off interactable without changing alpha

I notice that there is a default script in unity 5 calls Canvas Group. I applied it on a button so i can turn off interactable when i need to. Then i found out when i play the app the button become half transparent as it is not interactable. I check through its components and all the alpha attributes are at 1. I did notice that unity do that itself but is there any way to set my own alpha? I do have a script on the button and all it does is turn on and off the interactable option. What else should i write to fix that auto alpha change and where should i write it? Start function? OnEnable?