How to call the async function which returns Future <bool> in the ternary function to have different colors based on the returned value?

Question

I want to use dark mode in my flutter calculator app. I used Dynamic Theme plugin to switch from dark to light mode.

Previously, I was using _darkmode variable through which I made the color of my button customized for dark and light mode. But whenever I closed my app its color used to get switched or mismatched combination of different colors appeared. And I thus wanted to solve this using shared preferences. So, if _darkMode variable is not present in SP then define it with False initially. And according to the SharedPreference get data I want to set the colors of the buttons. Also, I used a switch to set and change the Shared preference.

So this is my code:
init state where I am initially defining the _darkmode.

class _SimpleCalculatorState extends State<SimpleCalculator> {
Future<SharedPreferences> _prefs = SharedPreferences.getInstance(); // shared preferences
Future<bool> _darkmode;      // this variable to store in SP and for darkmode.

@override
void initState() {
    // ! init
    super.initState();
    _darkmode = _prefs.then((SharedPreferences prefs) {
    return (prefs.getBool('darkMode') ?? false);
    });
}

To set the values of darkmode varibale on shared preferences:

// to set the values on SP
void setBoolToSP(bool boolValue) async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.setBool('darkMode', boolValue);
}

To get the value of darkmode varibale from shared preferences:

// to get values from sp
getBoolValuesSP() async {
    try {
        SharedPreferences prefs = await SharedPreferences.getInstance();
        print("inside getboolvaluesf");
        return prefs.getBool('darkMode');
    } catch (e) {
        print("getbool" + e);
    }
}

So, now I want to call this getBoolValuesSP() to here so that i can dynamically change the colors of the buttons based on values of _darkMode variable:

child: FlatButton(
    // ! here
    color: getBoolValuesSP()   // here
        ? (buttonColor != Colors.white ? buttonColor : Colors.black54)
        : buttonColor,
  }

But I'm getting an error like "A value of type 'bool' can't be assigned to a variable of type 'Future"

and I'm using a switch to toggle the dark and light mode.

Switch(
   activeColor: Colors.orange,
   inactiveThumbColor: Colors.black,
   value: _darkMode, // !
   onChanged: (value) {
       setState(() {
       DynamicTheme.of(context).setBrightness(
       Theme.of(context).brightness == Brightness.dark ? Brightness.light : Brightness.dark);
                    
       darkMode = !darkMode;
       setBoolToSF(darkMode);
       print("check    " + darkMode.toString());
   });
})

can anyone tell me how to call the getBoolValuesSP in the color and how to dynamically change the colors of buttons using Shared preference?