Unity Firebase: Can't change the color of an Image on RegistrationComplete

Hi, I would like to change the color of an Image when I register the user but the color is changing only in the inspector... And also I can't Invoke unity events in (task.isCompleted)

     public void Registration()
     {
    
         Auth.CreateUserWithEmailAndPasswordAsync("emai2l@gmail.com", "password")
             .ContinueWith((task =>
         {
             if (task.IsCanceled)
             {
                 Firebase.FirebaseException e =
                 task.Exception.Flatten().InnerExceptions[0] as Firebase.FirebaseException;
                 GetAuthError((AuthError)e.ErrorCode);
                 return;
             }
 
             if (task.IsFaulted)
             {
                 Firebase.FirebaseException e =
                 task.Exception.Flatten().InnerExceptions[0] as Firebase.FirebaseException;
                 GetAuthError((AuthError)e.ErrorCode);
                 return;
             }
 
             if (task.IsCompleted)
             {
                 img.color = Color.red; // <== THIS IS THE IMAGE
                 Debug.Log("Registration Complete");
                 
                 return;
             }
 
         }));
     }

Her's a short video: https://giphy.com/gifs/fAPTd80taCSq1QRMOd

Basically on registration complete I would like to give feedback to the user.. I tried to set a bool to true and then on Update to change the color and it worked but is there a more efficient way? Thank you!