Material.SetColor only works in Start function?

Hey guys,

I am making a virtual mixing console. Currently I am trying to change the color of a certain channel fader when the user presses the appropriate key (1 for channel 1, etc).

I start by declaring my Materials (one for each fader):

 public Material fader1Material;
 public Material fader2Material;
 public Material masterMaterial;

Then initializing them as white:

 //Initalize Fader Colours
 
 masterMaterial.SetColor("_Color", Color.white);
 fader1Material.SetColor("_Color", Color.white);
 fader2Material.SetColor("_Color", Color.white);

However, if I alter the Material's color anywhere outside of the start function, it does not change color (This is in update):

 if (Input.GetKey(KeyCode.Alpha1))
         {
 
             fader1Material.SetColor("_Color", Color.black);
             ChangeChannel(1);
             
 
         }

It does not throw an error, just doesn't work as intended. Pressing '1' successfully calls ChangeChannel(), but the color fails to change.

Any help would be appreciated!