FormBuilderDateTimePicker: how to customize colors?

Question

I use the formbuilder package and I have troubles to customize the colors of the pop up to select a time of FormBuilderDateTimePicker since FormBuilderCupertinoDateTimePicker is depreceted.

With the FormBuilderCupertinoDateTimePicker I could set the colors used in the pop up to select the time in timePickerTheme and it worked fine:

FormBuilderCupertinoDateTimePicker(
                  name: 'takeawayTimeEndEdit',
                  initialValue: initialValueTimeEndEdit,
                  decoration: decorationTextField("Tot *"),
                  inputType: CupertinoDateTimePickerInputType.time,
                  locale: (const Locale("nl")),
                  validator: FormBuilderValidators.required(),
                  timePickerTheme: const DatePickerTheme(
                      backgroundColor: ThemeColors.ymGreenOpac,
                      headerColor: ThemeColors.ymRed,
                      cancelStyle: TextStyle(color: ThemeColors.ymWhite),
                      doneStyle: TextStyle(color: ThemeColors.ymWhite),
                      itemStyle: TextStyle(
                        color: ThemeColors.ymDarkGrey,
                      )),
                ),

Now with the FormBuilderDateTimePicker I can't define a timePickerTheme anymore and I don't find any parameters that can customize the colors used.

So I tried to set the colors in ThemeData in my main file too like this (I am not very familiar with ThemeData so I defined every possibility that I thought could customize the colors of the FormBuilderDateTimePicker):

MaterialApp(
            localizationsDelegates: const [
              GlobalMaterialLocalizations.delegate,
            ],
            supportedLocales: const [Locale('en'), Locale('nl'), Locale('fr')],
            theme: ThemeData(
                timePickerTheme: const TimePickerThemeData(
                  backgroundColor: ThemeColors.ymGreenOpac,
                  hourMinuteColor: ThemeColors.ymRed,
                  dayPeriodColor: ThemeColors.ymRed,
                  dialHandColor: ThemeColors.ymRed,
                  dialBackgroundColor: ThemeColors.ymRed,
                  inputDecorationTheme: InputDecorationTheme(
                    filled: true,
                    fillColor: ThemeColors.ymRed,
                  ),
                ),
                cupertinoOverrideTheme: const CupertinoThemeData(
                  primaryColor: ThemeColors.ymRed,
                  primaryContrastingColor: ThemeColors.ymRed,
                  barBackgroundColor: ThemeColors.ymRed,
                ),
                scaffoldBackgroundColor: ThemeColors.ymGreenOpac,
                primaryColor: ThemeColors.ymRed,
                secondaryHeaderColor: ThemeColors.ymRed,
                canvasColor: ThemeColors.ymRed),
            onGenerateRoute: RouteGenerator.generateRoute,
            scrollBehavior: MyCustomScrollBehavior(),
            debugShowCheckedModeBanner: false,
            navigatorKey:
                navigatorKey, //needed to create popups without context
            initialRoute: Routes.languageChoice,
          ),

But this doesn't give me the result I am searching for. Can anyone help me out with this?